SYMPOSIUM ON ONCOLOGY PRACTICE: HEMATOLOGICAL CHRONIC MALIGNANCIES. Chronic Myeloid Leukemia: Diagnosis and Treatment

Transcription

1 SYMPOSIUM ON ONCOLOGY PRACTICE: HEMATOLOGICAL CHRONIC MALIGNANCIES MYELOID LEUKEMIA Chronic Myeloid Leukemia: Diagnosis and Treatment ALFONSO QUINTÁS-CARDAMA, MD, AND JORGE E. CORTES, MD Chronic myeloid leukemia (CML) has become a model in research and management among malignant disorders. Since the discovery of the presence of a unique and constant chromosomal abnormality slightly more than 40 years ago, substantial progress has been made in the understanding of the biology of the disease. This progress has translated into significant improvement in the longterm prognosis of patients with this disease. This change came first with the use of stem cell transplantation and interferon alfa, but recently it has opened the era of molecularly targeted therapies. Imatinib, a potent and selective tyrosine kinase inhibitor, may be the best example of our attempts to identify molecular abnormalities and develop drugs directed specifically at them. Furthermore, the understanding of at least some of the mechanisms of resistance to imatinib has led to rapid development of new agents that may overcome this resistance. The outlook today for patients with CML is much brighter than just a few years ago. It is our hope that this fascinating journey in CML can be replicated in other malignancies. In this article, we review our current understanding of this disease. Mayo Clin Proc. 2006;81(7): ALL = acute lymphoblastic leukemia; AML = acute myeloid leukemia; AP = accelerated phase; ATP = adenosine triphosphate; BP = blast phase; CCGR = complete cytogenetic response; CHR = complete hematologic response; CML = chronic myeloid leukemia; CP = chronic phase; Grb2 = growth factor receptor bound protein 2; IC 50 = inhibitory concentration that results in a 50% reduction in proliferation; MCGR= major cytogenetic response; MMR = major molecular response; MUD = matched unrelated donor; Ph = Philadelphia; PI3K = phosphatidylinositol 3-kinase; RT-PCR = reverse transcriptase polymerase chain reaction; SCT = stem cell transplantation; STAT = signal transducer and activator of transcription; TKI = tyrosine kinase inhibitor; WBC = white blood cell Chronic myeloid leukemia (CML) is a clonal myeloproliferative disorder of a pluripotent stem cell 1 first described by John Hughes Bennett in 1845 at The Royal Infirmary of Edinburgh. 2 It has been classified as a myeloproliferative disorder along with agnogenic myeloid metaplasia, polycythemia vera, and essential thrombocythemia. 3 Chronic myeloid leukemia was the first malignancy that had a specific chromosomal abnormality uniquely linked to it after the discovery of a minute chromosome now known as the Philadelphia (Ph) chromosome, 4 later defined to result from a t(9;22) reciprocal chromosomal translocation. 5 Of critical importance was the demonstration that this translocation involved the ABL1 (Abelson) protooncogene in chromosome 9 and the BCR (breakpoint cluster region) gene in chromosome 22. 6,7 Since then, a constant stream of clinical and basic advances has made CML one of the most extensively studied human malignancies. The introduction of rationally designed small molecules that target the tyrosine kinase activity of Bcr-Abl in the treatment of CML has pioneered the development of targeted therapies in cancer medicine. In this review, we summarize the current knowledge of the molecular biology of CML and discuss the current treatment modalities, including the important historical role of recombinant interferon alfa, the development of imatinib mesylate and the new tyrosine kinase inhibitors (TKIs), stem cell transplantation (SCT), and other novel therapeutic approaches still in preclinical or early clinical development. EPIDEMIOLOGY AND ETIOLOGY Chronic myeloid leukemia is a rare disease worldwide. Approximately 4600 new cases of CML were diagnosed in 2004 in the United States, among 33,400 new cases of leukemia. Hence, CML represents 14% of all leukemias and 20% of adult leukemias. The annual incidence is 1.6 cases per 100,000 adults, 8 with a slight male preponderance (male-female ratio, 1.4:1). The median age at diagnosis is 65 years. In contrast, CML is exceedingly rare in children, and its incidence increases with age. 9 There are no known hereditary, familial, geographic, ethnic, or economic associations with CML; therefore, the disease is neither preventable nor inherited. In most patients, the factor responsible for the induction of the Ph chromosome is unknown, although CML has been observed with increased frequency in individuals exposed to the atom bomb explosions in Japan in 1945, in radiologists, and in patients with ankylosing spondylitis treated with radiation therapy. 10 CLINICAL PRESENTATION AND NATURAL HISTORY Classically, 3 phases of disease progression are recognized in CML: chronic phase (CP), accelerated phase (AP), and blast phase (BP) (Table 1). Currently, nearly 90% of patients with CML have their conditions diagnosed in the CP. Frequently, the diagnosis is made incidentally after a rou- From the Department of Leukemia, The University of Texas, M. D. Anderson Cancer Center, Houston, Tex. Dr Cortes has research grant support from Novartis, BMS, The Vaccine Company, ChemGenex Pharmaceuticals, Ltd, and Breakthrough Therapeutics. Address correspondence to Jorge E. Cortes, MD, Department of Leukemia, The University of Texas, M. D. Anderson Cancer Center, 1515 Holcombe Blvd, Unit 428, Houston, TX ( jcortes@mdanderson.org). Individual reprints of this article and a bound booklet of the entire Symposium on Oncology Practice: Hematological Malignancies will be available for purchase from our Web site Mayo Foundation for Medical Education and Research Mayo Clin Proc. July 2006;81(7):

2 TABLE 1. Criteria for Accelerated Phase According to 3 Frequently Used Classifications* MDACC 11 IBMTR 12 WHO 13 Blasts (%) Blasts and promyelocytes (%) NA Basophils (%) Platelets ( 10 9 /L) <100 Unresponsive increase or <100 or >1000 unresponsive persistent decrease to treatment Cytogenetics CE CE CE not at the time of diagnosis White blood cell NA Difficult to control or NA doubling in <5 d Anemia NA Unresponsive NA Splenomegaly NA Increasing NA Other NA Chloromas, myelofibrosis Megakaryocyte proliferation, fibrosis *CE = clonal evolution; IBMTR = International Bone Marrow Transplant Registry; MDACC = M. D. Anderson Cancer Center; NA = not applicable; WHO = World Health Organization. Blast phase of 20% or more blasts ( 30% for MDACC and IBMTR). Basophils and eosinophils. tine complete blood cell count is performed for unrelated reasons. This is due to the fact that patients with CML-CP have a competent immune system and may remain asymptomatic for prolonged periods. When symptoms appear, they are generally related to the expansion of CML cells and consist typically of malaise, weight loss, and discomfort caused by splenomegaly. 14 Leukocytosis is a common feature of CP, and the white blood cell (WBC) count can be as high as /L, leading in rare instances to signs and symptoms of hyperviscosity, such as retinal hemorrhage, priapism, cerebrovascular accidents, tinnitus, confusion, and stupor. After a median of 3 to 5 years, untreated patients with CML-CP inevitably progress to CML-BP, an aggressive form of acute leukemia highly refractory to chemotherapy that is rapidly fatal. 15 The risk of transformation to CML-BP is estimated at 3% to 4% per year. 15,16 Chronic myeloid leukemia-ap is characterized by an increasing arrest of maturation that usually heralds transformation to CML-BP. Different criteria have been used to define CML-AP. One commonly used classification defines AP as the presence of at least 1 of the following hematologic features: 15% or more blasts, 30% or more blasts plus promyelocytes, 20% or more basophils, or platelet counts lower than /L unrelated to therapy. 17 Of note, most classification systems for CML-AP and CML-BP proposed throughout the years in the literature were developed before the introduction of imatinib, and some, such as the recent World Health Organization proposal, 13 have not been validated in clinical studies and therefore may lack clinical importance. 18 Most discrepancies among different classifications relate to the use of slightly different cutoffs for hematologic values and other additional minor criteria. Although patients may become symptomatic, the transition from CML-CP to CML-AP is usually subclinical, and laboratory monitoring is necessary for detection of disease progression. The median survival for patients with CML- AP is 1 to 2 years. 19 Most patients CML will remain in AP for 4 to 6 months before progressing to BP. 20,21 Classic criteria define CML-BP by the demonstration of at least 30% of blasts in the peripheral blood or the bone marrow or the presence of extramedullary blastic foci. The World Health Organization classification proposes a reduction from 30% or more to 20% or more blasts for the diagnosis of CML-BP. Clinically, most patients with CML-BP experience signs and symptoms related to increasing tumor burden, including inability to control WBC counts with previously stable doses of medication, marked constitutional symptoms (fever, night sweats, anorexia, malaise, weight loss), splenic infarcts due to massive splenomegaly, bone pain, and increased risk of infections and bleeding. The presence of cytogenetic abnormalities in addition to the Ph chromosome (ie, clonal evolution) involves most frequently trisomy 8, isochromosome 17, and duplicate Ph chromosome and has been considered a criterion of CML- AP. However, patients who are classified as having CML- AP based solely on the presence of clonal evolution appear to fare better than those whose conditions were diagnosed on the basis of other clinical features. Immunophenotypically, CML-BP can be characterized by myeloid or lymphoid phenotype. In rare instances, blast cells can be biphenotypic with a mixed lymphoblastic-myeloblastic lineage. 19,22 Lymphoid CML-BP occurs in 20% to 30% of patients, myeloid in 50%, and undifferentiated in 25%. 22,23 Median survival of patients with lymphoid CML- BP is 3 to 6 months, with patients with lymphoid CML-BP having a slightly better prognosis than those with myeloid phenotype. 974 Mayo Clin Proc. July 2006;81(7):

3 LABORATORY AND PATHOLOGICAL FEATURES Laboratory findings in CML include leukocytosis with a remarkable left shift, basophilia, and eosinophilia. Platelet count may be either high or low, and mild anemia is commonly observed. The leukocyte alkaline phosphatase activity is reduced, although phagocytic function remains essentially normal. 24 Low values may also be observed in agnogenic myeloid metaplasia, whereas activity may increase with infection, clinical remission, or at the onset of BP. The increase in the size of the WBC pool is reflected by marked elevation of serum B 12 levels and unsaturated B 12 - binding capacity. During transformation to CML-BP, circulating basophil levels, histamine levels, or both often increase, but the causative factors and importance of these phenomena remain unknown. 25 The bone marrow of patients with CML is notoriously hypercellular and devoid of fat. 26 In fact, it can be hypothesized that the primary biologic defect in CML is not unregulated proliferation of leukemic stem cells but rather discordant maturation, wherein a slight delay in cell maturation within the myeloid compartment results in increased myeloid mass. 27 All stages of myeloid maturation are present, with predominance of myelocytes. In CP, the sum of myeloblasts and promyelocytes usually accounts for less than 10% of the marrow cellularity. A decrease in apoptosis of myeloid cells contributes to the expansion of this compartment and defective adherence of immature CML cells to marrow stromal cells in vitro, 28 with subsequent early release into the circulation. Megakaryocytes may be increased, and Gaucher-like cells can be observed in 10% of cases. 29 As CML progresses, varying degrees of reticulin fibrosis may be seen, 30 likely a result of the interaction between the proliferative clone of megakaryocytes and cytokines, such as platelet-derived growth factor, transforming growth factor β, and basic fibroblastic growth factor, whose plasma levels are significantly increased in CML. 31 Of note, these cytokines play an important role modulating angiogenesis, and characteristically the bone marrow from patients with CML shows the highest number of blood vessels and largest vascular area of all leukemias. 31 Blastic cells from patients with lymphoid CML-BP express terminal deoxynucleotidyl transferase, an enzyme that catalyzes the polymerization of deoxynucleoside triphosphates and is mainly found in poorly differentiated B and T cells. 32 In most cases of lymphoid CML-BP, blasts exhibit a B-cell immunophenotype, expressing CD10, CD19, and CD22. In contrast, myeloid CML-BP closely resembles acute myeloid leukemia (AML), and blasts stain with myeloperoxidase and express myeloid markers such as CD13, CD33, and CD117. Frequently, myeloid markers such as CD13 and CD33 may be expressed in patients with lymphoid CML-BP. Rare cases of megakaryoblastic, 33 erythroblastic, 34 and mastoblastic 35 transformation have been reported. PROGNOSTIC SYSTEMS Because of the difference in clinical aggressiveness between the initial CP and advanced phases of CML and because the prognosis in CML can vary significantly even among patients in the same phase of the disease, several risk stratification strategies have been developed in an attempt to prognosticate and guide patient management. The system most extensively used is the Sokal score, which was derived from 813 patients with CML collected from 6 European and American series in the 1960s and 1970s. 36 In this system, the hazard ratio for death is calculated from baseline patient and disease characteristics using the following formula: λ i (+)/λ o (t) = Exp (age 43.4) (spleen 7.51) [(platelets/700) ] (blasts 2.10). This scoring system establishes 3 prognostic groups with hazard ratios of less than 0.8, 0.8 to 1.2, and more than 1.2 and median survivals of approximately 2.5, 3.5, and 4.5 years, respectively. 36 Of note, most of the patients from whom the Sokal score was derived were treated with therapies currently not in use, such as busulfan, intensive chemotherapy, and splenectomy. However, several studies performed in the 1990s have demonstrated the applicability of this system in more modern series. Of 625 patients with CML-CP treated with chemotherapy in one study, 168 (27%) were high risk and had a 2- year actuarial survival of 70% and a subsequent probability of death of approximately 30% per year. In contrast, the low-risk group had a 2-year actuarial survival of 91% and a subsequent risk of death of approximately 17% per year. 37 The Sokal system has several limitations. First, in asymptomatic patients whose disease is detectable only by molecular testing, lead-time bias can be substantial relative to those whose conditions are diagnosed after presenting with symptoms. Second, the use of more refined and potent therapeutic modalities in CML, such as imatinib, has been associated with the loss of predictive value of some prognostic factors. 38 Still, the Sokal score identifies patients with significantly different probabilities of response to imatinib, although patients with high-risk scores now have a much better outcome. Other scoring systems have been proposed that may be more applicable to patients treated with interferon alfa. The best-characterized and most widely used is the Hasford score, 39 which considers patient age, platelet count, peripheral blast count, spleen size, eosinophils, and basophils to determine risk. Some analyses have suggested that this scoring system is less predictive among patients treated Mayo Clin Proc. July 2006;81(7):

4 with imatinib, but others have found it still useful. Finally, the Gratwohl score system has been developed specifically for patients undergoing SCT. 40 CYTOGENETICS A conclusive diagnosis of CML relies on cytogenetic and molecular testing to identify the t(9;22)(q34.1;q11.21) and/ or the BCR-ABL1 hybrid gene, which is pathognomonic of this disease. 4,5 The Ph chromosome results from the balanced translocation of cytogenetic material after a break on chromosome 9 at band q34.1 that transposes the 3 segment of the ABL1 gene to the 5 segment of the BCR gene on chromosome 22 at band q The Ph chromosome is detected in 95% of patients with CML and in 5% of children and 15% to 30% of adults with acute lymphoblastic leukemia (ALL). In addition, approximately 2% of patients with newly diagnosed AML can present with this cytogenetic abnormality. 41 Occasionally, translocations that involve 3 or more chromosomes occur and are termed variant Ph chromosome translocations. 42,43 Although initially thought to confer poor prognosis, 44 recent data in patients treated with imatinib have demonstrated that variant translocations are associated with a similar prognosis compared with patients with the classic Ph chromosome. 45 In 5% of patients with typical CML phenotype, the Ph chromosome is not detectable but harbors the BCR-ABL1 rearrangement. 46 These patients have the same biology and outcome as those who express the Ph chromosome. Among the 5% to 10% of patients with CML clinical features who do not express the Ph chromosome, 30% to 50% have molecular evidence of the rearrangement involving BCR and ABL1. Those who do not express this molecular abnormality (ie, true Ph chromosome negative) are called atypical CML and have a different prognosis and treatment. 47 The characteristics and management of atypical CML are not covered any further in this article. Little is known about the mechanisms involved in transformation to CML-BP, but the acquisition of additional cytogenetic abnormalities, referred to as clonal evolution, in Ph chromosome positive cells has been thought to play a prime role in CML progression. The most frequent secondary cytogenetic abnormalities encountered in patients with clonal evolution are trisomy 8, isochromosome 17, and duplicate Ph chromosome, which have been linked to c-myc overexpression, loss of 17p, and BCR-ABL1 overexpression, respectively Other cytogenetic aberrancies, such as trisomy 19, trisomy 21, trisomy 17, and deletion 7, have been implicated in less than 10% of cases of clonal evolution. 51,52 These genetic lesions are more frequently associated with myeloid than with lymphoid CML-BP. Nonetheless, a clear correlation between the development of these molecular features and disease progression has not been established yet. In addition, other molecular events, such as deletion or inactivation of p53, 53 p16, 54 and the retinoblastoma gene product 55 have been associated with disease transformation, but like overexpression of EVI-1, 56 these are relatively infrequent and therefore not specific to CML-BP. 57 Recently, it was suggested that progression of CML to BP probably involves several events in primitive progenitors, including BCR- ABL1 amplification, acquisition of resistance to apoptosis, genomic instability, escape from innate and adaptive immune responses, and activation of β-catenin in granulocyte-macrophage progenitors, resulting in the acquisition of self-renewal capacity. 58 Gene methylation has also been associated with progression in CML The Pa promoter of ABL1 and the p15 promoter are hypermethylated in 81% and 24% of patients, respectively. Interestingly, hypermethylation of p15, but not of the Pa promoter, is associated with disease progression. Methylation of the cadherin- 13 gene occurs at an early stage in CML and is associated with high-risk features and lower probability of response to interferon alfa. 62 Cytogenetic aberrancies have been reported occasionally in Ph chromosome negative cells during treatment with interferon alfa and, more recently, with imatinib. These aberrancies do not represent clonal evolution because they occur in cells without the Ph chromosome and should not be considered as part of the definition of AP. The importance of these events is currently unknown. 63 The most common such cytogenetic abnormalities include trisomy 8, monosomy 5 or 7, and deletion 20q These abnormalities frequently regress spontaneously, and it has been suggested that patients with these abnormalities have similar long-term outcome as patients without such abnormalities. However, occasional cases of progression to AML or myelodysplastic syndrome have been reported. MOLECULAR BIOLOGY OF BCR-ABL1 The ABL1 gene is the human homologue of the v-abl oncogene harbored by the Abelson murine leukemia virus, 67 and it encodes a nonreceptor tyrosine kinase (Figure 1). 68 In turn, BCR encodes a protein with serine threonine kinase activity. The fusion of these 2 genes results in the activation of the c-abl protooncogene to its oncogenic form. 69,70 The breakpoints within the ABL1 gene at 9q34 map to an area spanning more than 300 kilobase (kb) at its 5 end occur upstream of exon Ib, downstream of exon Ia, or, more frequently, between the two. 71 Alternatively, breakpoints within BCR localize to 3 main breakpoint cluster regions. In most patients with CML and a third of those with Ph chromosome positive ALL, the break occurs 976 Mayo Clin Proc. July 2006;81(7):

5 FIGURE 1. Activation of signal transduction pathways by BCR/ABL. AKT = protein kinase B; ERK = extracellular signal-regulated kinase; JAK = Janus kinase; MEK = mitogen-activated protein kinase kinase; PI3K = phosphatidylinositol 3-kinase; SAPK = stress-activated protein kinase; STAT = signal transducer and activator of transcription. within a 5.8-kb area spanning BCR exons e12-e16 (formerly called b1-b5), referred to as the major breakpoint cluster region (M-bcr). Because of alternative splicing, a fusion transcript with either b2a2 or b3a2 junctions can result and will give rise to a 210-kd hybrid protein (p210 BCR-ABL ). 72,73 The clinical features and response to treatment are apparently similar for both transcripts. In two thirds of patients with Ph chromosome positive ALL and rarely in CML, the breakpoints within BCR localize to an area of 54.4 kb between exons e2 and e2, termed the minor breakpoint cluster region (m-bcr), giving rise to an e1a2 messenger RNA that is translated to a 190-kd protein (p190 BCR-ABL ). Patients with CML who carry this transcript can present with marked monocytosis and may have a worse prognosis than those with the typical p A third breakpoint cluster region (µ-bcr) downstream of exon 19 has been identified, giving rise to a 230-kd fusion protein (p230 BCR-ABL ) linked to cases of chronic neutrophilic leukemia. 75 Although all 3 transcripts can induce a CML-like disorder in mice, p230 BCR-ABL has reduced tyrosine kinase activity relative to p190 BCR-ABL76 and confers only partial growth factor independence, which parallels the milder clinical course of chronic neutrophilic leukemia. 75 All the isoforms of Bcr-Abl have an active and an inactive configuration. Interestingly, using reverse transcriptase polymerase chain reaction (RT-PCR) with a sensitivity of approximately 10 8, the BCR-ABL1 chimerism has been identified in up to 25% to 30% of presumably healthy adults. 77,78 One hypothesis to explain this phenomenon is that BCR-ABL1 might not be the sole genetic lesion necessary for the development of CML. JunB is a component of the activator protein 1 family of transcription factors 79 Modifications of JunB expression may have a role in the pathogenesis of CML by modulating the initiation, progression, and maintenance of the myeloid differentiation program. 80 A recent report in which transgenic mice specifically lacking JunB in the myeloid lineage (JunB / Ubi-JunB mice) develop a myeloproliferative disorder that resembles human CML, including progression to BP, seems to support the latter hypothesis. 81 Several biological models, such as BCR-ABL1 expressing CD34 + cells in culture 82,83 or retrovirally transduced BCR-ABL1 + mouse cells, 84 have demonstrated that BCR- ABL1 is an oncogene that promotes CML pathogenesis. Numerous pathways are activated in BCR-ABL1 expressing cells, 85 and phosphorylation at the Y177 site of BCR is essential for BCR-ABL1 leukemogenesis. 86,87 This residue constitutes a high-affinity docking site for the SH2 domain of growth factor receptor bound protein 2 (Grb2). In turn, Grb2 recruits SOS (a guanine-nucleotide exchanger of RAS) and the scaffold adapter Grb2-associated binding protein 2 (GAB2) through its SH3 domain. Phosphorylation of GAB2 leads to recruitment of phosphatidylinositol 3-kinase (PI3K) and SHP2 (also known as PTPN11), whereas SOS activates RAS. 88 Mutation of Y177 to phenylalanine (Y177F) largely abolishes Grb2 binding and abrogates Bcr-Abl induced RAS activation. Therefore, despite Mayo Clin Proc. July 2006;81(7):

6 preservation of the kinase activity of Abl, the Y177F mutant impedes the transformation of primary bone marrow cultures. 86 In an SCT model of CML, BCR-ABL1 Y177F has a greatly reduced ability to induce a myeloproliferative disorder in mice. 89 Of note, SHP2 is required for normal activation of the RAS extracellular signal-regulated kinase pathway that most receptor tyrosine kinases signal through. 88 Bcr-Abl also phosphorylates the Src kinases Lyn, Hck, and Fgr. Once phosphorylated, Hck activates signal transducer and activator of transcription (STAT) 5. 90,91 Importantly, overexpression of Hck/Lyn has been linked with disease progression, particularly with a lymphoid phenotype. 92 Therefore, Bcr-Abl promotes hematopoietic cell transformation mainly through RAS, PI3K, and STAT 5 activation. All these elements have been shown to up-regulate the expression of cyclin D1, thus inducing cellcycle progression from G 1 to S phase. 93,94 When BCR- ABL1 positive K562 cells were induced to express dominant negative forms of RAS, PI3K, or STAT 5, marked apoptosis was observed in cells coexpressing 2 of 3 dominant negative mutants in any combination. 95 Notably, Bcr- Abl also enhances SET expression, particularly during progression to BP. 96 SET is a nucleus/cytoplasm-localized phosphoprotein that potently inhibits the tumor suppressor protein phosphatase 2A (PP2A). In turn, PP2A is a phosphatase that regulates cell proliferation, survival, and differentiation. 97 Some of the elements involved in Bcr-Abl signal transduction have been sought as therapeutic targets in CML. TREATMENT The treatment of CML has experienced a great degree of refinement during the past few years. Until recently, interferon alfa and SCT were the only therapeutic options for patients with CML. Currently, SCT still remains a valid option, particularly for patients who do not respond appropriately to TKIs, and still remains a potentially curative therapeutic modality. However, the explosion of the field of molecularly targeted TKIs in recent years led by imatinib mesylate has brought about a change in the natural history of the disease and in the therapeutic approach to CML. INTERFERON Recombinant human interferon alfa has shown significant antitumor and immunomodulatory activity in the treatment of CML. 98,99 Major cytogenetic responses (MCGRs) (<35% Ph chromosome positive cells) have been reported in up to 40% of patients and complete cytogenetic responses (CCGRs) (0% Ph chromosome positive cells) in up to 25%. 100 The addition of cytarabine resulted in a significantly higher probability of a CCGR in up to 35% of patients The achievement of a CCGR is associated with improved survival, with 78% of patients who achieved a CCGR alive at 10 years, establishing the achievement of a CCGR as the therapeutic goal in the interferon alfa era. 106 Furthermore, approximately 30% of patients in CCGR also had undetectable disease by PCR (ie, complete molecular remission); none of them has relapsed after a median follow-up of 10 years and are therefore probably cured. 106,107 Interestingly, 40% to 60% of those in CCGR with the presence of minimal residual disease at the molecular level have not relapsed after 10 years. This has been attributed to interferon alfa induced immune modulation, such as the presence of cytotoxic T lymphocytes specific for PR1, a peptide derived from proteinase 3, which is overexpressed in CML cells. This phenomenon has been demonstrated in patients in complete remission after interferon alfa therapy and SCT but not in those who fail to achieve CCGR or those treated with chemotherapy. 108 STEM CELL TRANSPLANTATION Stem cell transplantation remains an important treatment option for patients with CML, particularly younger individuals with HLA-identical siblings. Initially, SCT was thought to render the best outcomes when performed within 12 months from CML diagnosis. It has been reported that SCT performed within the first 24 months, and in some reports within the first 36 months, from diagnosis may have similar outcomes. 40 Although it was initially suggested that prior interferon alfa therapy adversely affected the outcome after SCT, 109 subsequent trials demonstrated that this adverse effect was nonexistent, and current evidence suggests that prior exposure to imatinib does not affect the outcome either. 114,115 Current registry data revealed that the post-sct mortality within the first year is 10% to 20% even in patients who underwent transplantation in optimal conditions (ie, HLA-matched sibling, first CP <1 year from diagnosis, age <40 years). In addition, only one third to one half of patients may have a suitable HLA-matched sibling, and stringent inclusion criteria, such as age, adequate organ function, and performance status, may preclude the possibility of SCT in a large proportion of patients. A strategy to overcome the lack of suitable donors is the use of matched unrelated donors (MUDs). 116 Unfortunately, the survival rate of patients undergoing MUD SCT is still lower when compared with those receiving grafts from HLA-matched siblings. The outcome of MUD SCT may be improved by careful molecular typing, particularly for HLA-A, HLA-B, and HLA-DRB However, the use of stringent typing criteria is inevitably linked to a lower probability of finding an adequate donor. In addition, SCT is fraught with risks such as graft-vs-host disease, veno-occlusive disease, life- 978 Mayo Clin Proc. July 2006;81(7):

7 threatening infections, risk of secondary malignancy, and poorer overall quality of life. 117 Also, the risk of late relapse is being increasingly recognized. A recent series analyzed the long-term follow-up of 89 patients who underwent transplantation at a single institution. 118 After more than 10 years of follow-up, 28 patients (31%) were alive. The mean time to hematologic or cytogenetic relapse was 7.7 years, with 5 patients relapsing more than 10 years after SCT. In a recent study by the Seattle group, 131 patients with early CML-CP with a median age of 43 years (range, years) received targeted busulfan and cyclophosphamide as a conditioning regimen. At 3 years, the projected nonrelapse mortality rate was 14%, and 78% were projected to be alive and free of disease. However, 60% of survivors had extensive chronic graft-vs-host disease 1 year after transplantation, although only 10% had a Karnofsky score less than 80%. Notably, 11% of patients had minimal residual disease documented by PCR but had not relapsed at the time of the report. 119 In contrast, patients with advanced phase CML who undergo SCT have a 5-year survival probability of 40% to 60% in the AP and 10% to 20% in the BP. Notably, the long-term outcome of patients with CML-BP who achieve a second CP and who are undergoing SCT appears to be similar to that of patients with CML-AP who undergo transplantation. The long-term disease-free survival rate after MUD SCT for young patients in the early CP stage of disease is 57% compared with 67% in patients receiving grafts from HLA-matched siblings. 120 The incorporation of molecular matching in recent years has decreased the rate of graft-vshost disease and improved the probability of long-term survival in patients undergoing MUD SCT. Reduced-intensity conditioning regimens have been used as a means to make SCT available to a broader number of patients who otherwise would be ineligible for standard SCT. This approach takes advantage of the ability of the T cells harbored in the graft to eliminate the CML cells (graft-vs-leukemia effect) as opposed to obtaining this effect by using ablative cytotoxic chemotherapy. This strategy increases tolerability and decreases morbidity and mortality significantly. Long-term results with reducedintensity conditioning regimens are not yet available, but early results in small series (frequently including still mostly young patients) report disease-free survival as high as 85% at 70 months. 121 In contrast, a recent study from the European Bone Marrow Transplant Registry reports a 3- year overall survival rate of 58% and a progression-free survival rate of 37%. 122 Patients with minimal residual disease by PCR 12 months after SCT have a risk of relapse of 30% to 40% compared with less than 5% for those with negative PCR results. 123 However, relapse can be frequently managed successfully with donor lymphocyte infusion in up to 70% of patients who relapse in the CP, particularly when administered at the time of molecular relapse. Alternatively, imatinib can be used in the post- SCT relapse setting and induces CCGR in more than 40% of patients treated in the CP. 124 IMATINIB MESYLATE Imatinib mesylate (Gleevec) is an orally bioavailable 2- phenylaminopyrimidine with targeted inhibitory activity against the constitutively active tyrosine kinase of the Bcr- Abl chimeric fusion protein. In addition, imatinib inhibits other kinases, such as c-kit, platelet-derived growth factor α and β, and Abl-related gene (ARG). 125,126 Imatinib has become the standard therapy for CML because of its remarkable activity and mild toxicity profile. In a phase 1 dose-finding study in patients who were intolerant to or in whom interferon alfa based therapy failed, daily doses of 25 to 1000 mg were investigated. Responses among patients receiving doses lower than 250 mg/d were rare, in contrast to 98% of patients receiving a dose of at least 300 mg/d who achieved a complete hematologic response (CHR), including 54% who attained a cytogenetic response. Of note, no dose-limiting toxicity was identified, and the maximum tolerated dose was not reached. 127 A dosage of 400 mg/d was selected for a subsequent phase 2 study, including 454 patients with late CP disease who were intolerant to or in whom interferon alfa therapy failed. 128 Recently updated data showed that 96% of patients had achieved a CHR and 55% a CCGR. After a median follow-up of 5 years, the overall survival rate was 79%. 128 This rate is in keeping with results from a recent single-institution study in which among 261 patients treated, 73% obtained a MCGR and 63% a CCGR. 129 After a median follow-up of 45 months, 86% of patients are alive, of whom 80% are free of progression. More than 90% of patients who achieved a CCGR maintained a major response. The BCR-ABL1/ABL1 ratio by nested PCR was less than 0.05% in 31% and undetectable in 15% of patients. 129 In the prospective, multicenter phase 3 International Randomized Study of Interferon and STI571, the efficacy of imatinib was compared with the combination of interferon alfa and low-dose cytarabine in patients with newly diagnosed CML-CP. 130 Patients treated with imatinib (n=553) or interferon alfa and low-dose cytarabine (n=553) were allowed to cross over to the alternative group if treatment failure or intolerance was demonstrated. 131 Imatinib therapy was superior to interferon alfa plus lowdose cytarabine regarding hematologic and cytogenetic responses, tolerability, and transformation to CML-AP. After a median follow-up of 54 months, the CHR, MCGR, and CCGR rates were 98%, 92%, and 86%, respectively. 132 Progression-free survival is estimated to be 84%, and only Mayo Clin Proc. July 2006;81(7):

8 1.0 Proportion surviving % Year Total Dead Imatinib Time from referral (y) FIGURE 2. Survival of patients with early chronic phase chronic myeloid leukemia treated at M. D. Anderson Cancer Center in different eras compared with those treated with imatinib. 6% of patients have progressed to AP or BP. The overall annual progression rate has declined to 1.5% in the fourth year of therapy, compared with 4.8% and 7.5% in the previous 2 years, suggesting that disease progression may plateau in the ensuing years. The depth of the response after 12 months of imatinib therapy has important implications regarding disease progression and relapse. In fact, in 97% of patients who had a 3-log or greater reduction in BCR- ABL transcript levels (ie, major molecular response [MMR]) at 12 months, the probability of remaining free of progression to AP or BP was 97% at 54 months compared with 89% for patients in CCGR but not in MMR and 72% for patients who did not achieve a CCGR at 12 months (P=.001). 132,133 In addition, the median BCR-ABL levels continue to decrease, with a mean log reduction at 48 months of 3.4 compared with 3.0 at 12 months. 134 Although this study did not document a survival advantage compared with the interferon alfa arm because of the crossover design, studies comparing survival of patients treated with imatinib with historical cohorts treated with interferon alfa based therapy demonstrate the anticipated survival advantage 135,136 (Figure 2). These results suggest that a trial of imatinib must be pursued in every patient before considering SCT. The results from the International Randomized Study of Interferon and STI571 have established imatinib 400 mg/d, as the standard therapy for CML. However, because the imatinib dosage selected after the dose-finding phase 1 study was based primarily on the excellent responses obtained when doses higher than 300 mg/d were used, it has been suggested that imatinib at higher dosages ( mg/d) might result in improved outcomes (Table 2). In one study, 36 patients with CML-CP in whom interferon alfa therapy failed were treated with imatinib 400 mg twice daily, resulting in a CCGR rate of 90%, compared with 48% in historical matched controls treated with standarddose therapy. 141 In addition, 56% of patients had an MMR, including 41% with undetectable levels. The toxicity profile was similar to that of imatinib, 400 mg, although there was a higher rate of grade 3 or higher myelosuppression. Several single-arm, phase 2 studies have used high-dose imatinib as the starting dose for patients with previously untreated CML-CP. These studies have documented a higher rate of CCGR of up to 95% and higher rates of molecular responses, particularly responses at the level of a 4-log or greater reduction in transcript levels. In addition, responses occur significantly earlier with high-dose compared with standard-dose therapy One study reported that by multivariate analysis, only treatment with high-dose imatinib (P=.02) was associated with achievement of an MMR and that achieving an MMR within the first 12 months of therapy is predictive of a durable cytogenetic remission. 142 Similarly, patients receiving the highest dose intensity during the first year of therapy have the highest probability of achieving a major molecular remission at 24 months (89%), whereas those receiving a median daily 980 Mayo Clin Proc. July 2006;81(7):

9 dosage less than 600 mg had a significantly lower probability both at 12 and at 24 months. 143 Thus, these studies suggest that high-dose imatinib may provide more and better remissions, but the results from ongoing randomized studies will determine whether high-dose imatinib provides only faster responses or whether these translate into prolonged progression-free and/or overall survival. Duration of Imatinib Therapy. Currently, no evidence exists to support the belief that patients taking imatinib can safely discontinue therapy once they achieve a complete molecular response. Most patients who have discontinued imatinib therapy have rapidly experienced both molecular and cytogenetic relapse, even when some had sustained undetectable levels of BCR-ABL for significant periods Recently, Rousselot et al 147 described 8 patients who discontinued use of imatinib after maintaining undetectable BCR-ABL levels for 24 months, 4 of whom still tested PCR negative after a follow-up of 8, 9, 12, and 13 months, respectively. All these patients had been treated with interferon alfa, suggesting that interferon alfa immunomodulatory effects may account for sustained and prolonged molecular responses observed on therapy discontinuation. It has been suggested that the most primitive quiescent leukemic progenitors are insensitive to imatinib in vitro and are responsible for CML relapse once the inhibitory pressure of imatinib is removed. 148 Emerging data suggest that resistance of quiescent cells to imatinib is indeed a Bcr-Abl dependent phenomenon. 149 Other potential mechanisms implicated in quiescent CML progenitors include expression of drug transport proteins such as PgP and Abcg2, atypical kinase domain mutations, 150 and BCR- ABL overexpression. 151 Monitoring of Imatinib Therapy and Minimal Residual Disease. The significant MMR rate observed with imatinib and its prognostic implications 152,153 have led to the redefinition of the therapeutic goals in CML. Rather than aiming solely at achieving a CCGR, 106,154 modern CML therapy should aim for the achievement of molecular responses. The long-term importance of molecular monitoring in CML has been best exemplified by patients undergoing SCT, in whom detection of BCR-ABL transcripts, particularly at high levels and 6 months after transplantation, confer a significantly higher risk of relapse. In these instances, prompt intervention (eg, donor lymphocyte infusion) has been effective. As mentioned earlier, among patients who achieve a CCGR with interferon alfa, the risk of relapse is minimal for those with low transcript levels. 107 Patients who achieve undetectable BCR-ABL transcripts by nested PCR have all had sustained cytogenetic remissions beyond 10 years. 106 In the imatinib setting, once a CCGR is attained, quantitative RT-PCR in peripheral blood samples at 3-month intervals is the mainstay of TABLE 2. Summary of Studies Using High-Dose Imatinib as Frontline Therapy for Early Chronic Phase Chronic Myeloid Leukemia* Dosage No. of CGCR MMR CMR Study (mg/d) patients (%) (%) (%) MDACC TIDEL RIGHT GIMEMA NA *CGCR = complete cytogenetic remission; CMR = complete molecular remission (BCR-ABL1 undetectable); GIMEMA = Gruppo Italiano Malattie Ematologiche dell Adulto; MDACC = M. D. Anderson Cancer Center; MMR = major molecular response (BCR-ABL1/ABL1 <0.05% or 3-log reduction); RIGHT = Rationale and Insight on Gleevec [imatinib] High-Dose Therapy; TIDEL = Therapeutic Intensification in de novo leukemia. monitoring for most patients. However, the lack of consistency in reporting BCR-ABL transcript levels has been a source of intense debate. A recent proposal aimed at the standardization of RT-PCR techniques and result reporting will greatly help this objective. According to this proposal, results will be converted by comparing analysis of standardized reference samples with a value of 0.1% corresponding to MMR in all laboratories. 155 After the patient has achieved a complete cytogenetic remission, RT-PCR should be performed every 3 months and a routine cytogenetic analysis every 12 months. 155 Fluorescence in situ hybridization in peripheral blood specimens can be used to monitor the cytogenetic responses among cytogenetic analyses. In addition, approximately 5% of patients who obtain a cytogenetic response develop clonal karyotypic abnormalities in Ph chromosome negative cells, primarily consistent with those encountered in myelodysplastic syndromes, although only rare cases of myelodysplastic syndrome or AML have been reported. 63 Although the long-term implications of these abnormalities are unknown, the risk of transformation to AML warrants careful follow-up of these patients. Imatinib Resistance. A subset of patients with CML will exhibit either primary or secondary resistance to imatinib. Primary resistance refers to patients never responding to imatinib, whereas secondary resistance occurs when a patient who had an initial response to imatinib eventually loses the response. Among patients treated in CP, the rate of resistance has been estimated to be less than 2% per year. Several mechanisms of resistance have been reported, many of them mostly in vitro or in selected patient samples, and their individual contribution to this phenomenon has not been completely defined. The most frequently identified mechanism of resistance is the development of mutations in the Abl tyrosine kinase domain. More than 40 different BCR-ABL point mutations have been reported thus far, and new ones continue to be described. 156 The region of the Abl kinase where mutations occur is Mayo Clin Proc. July 2006;81(7):

10 TABLE 3. Results With New Tyrosine Kinase Inhibitors After Failure of Imatinib in All Phases of CML* Hematologic response (%) No. of Agent and CML phase patients Overall Complete Overall Complete Phase 1 Cytogenetic response (%) Nilotinib 170 CP CE AP MyBP LyBP Dasatinib 171,172 CP AP MyBP LyBP Phase 2 Dasatinib CP AP MyBP LyBP and Ph+ ALL *AP = accelerated phase; CE = clonal evolution; CML = chronic myeloid leukemia; CP = chronic phase; LyBP = lymphoid blast phase; MyBP = myeloid blast phase; Ph+ ALL = Philadelphia chromosome positive acute lymphoblastic leukemia. critical in their ability to confer varying degrees of insensitivity to imatinib. In fact, ranges of 220 to more than 5000 nm/l in the inhibitory concentration that results in a 50% reduction in proliferation (IC 50 ) have been described in the various Bcr-Abl mutants. 157 The most frequent mutations are those that map to the P-loop region of the kinase domain The P-loop region is a glycine-rich structure that serves as a docking site for phosphate groups of adenosine triphosphate (ATP). G250E, Q252H, and the highly imatinib-insensitive Y253F and E255K mutations locate in this region. Despite not being directly involved in imatinib binding, these residues have been linked to poor prognosis in some series, with a median survival of 4 to 5 months Other series have refuted this notion. 164 The difference in these series may be due to several factors, including patient selection and the criteria used to select patients for screening for mutations. In addition, the first studies that suggested a poor outcome for patients with P-loop mutations did not address the management of patients after developing mutations, and it is now clear that several treatment strategies can overcome resistance through mutations. 165 Also, considering that individual mutations have different levels of resistance to imatinib and other agents, it is more appropriate to refer to individual mutations rather than grouping them. 155 The imatinib-insensitive T315I mutation occurs in a highly conserved gatekeeper threonine residue near the Bcr-Abl catalytic domain, thus leading to steric interference with imatinib binding. 161,162,166 Other mutations have been described mapping to the catalytic domain and the activation loop of Abl, impairing the ability of the kinase to adopt a close (inactive) spatial conformation necessary to bind to imatinib. 167 Despite the poor prognosis conferred by the T315I mutant, in vitro and clinical data suggest that other mutations may be clinically relevant. 168 Furthermore, other mechanisms of resistance, such as overexpression or amplification of the BCR-ABL message and/or protein, may influence the outcome of patients treated with imatinib. Recently, it was shown that activation of Src kinases and NF-κB may play a role in imatinib resistance in some patients. 92,169 TREATMENT STRATEGIES FOR THE FUTURE New Bcr-Abl Inhibitors. Several strategies are currently being developed to overcome imatinib resistance (Table 3). New Abl TKIs have been developed with enhanced potency and less stringent binding requirements and, in some cases, with inhibitory activity against other kinases involved in mechanisms of resistance to imatinib. In addition, new agents that block Bcr-Abl in a non ATPcompetitive manner may represent an alternative for patients who develop imatinib-insensitive Bcr-Abl kinase mutations. Nilotinib (AMN107). Nilotinib is a phenylamino-pyrimidine derivative with a 20- to 30-fold increased potency compared with imatinib against Bcr-Abl. Crystallographic models suggest that this increased potency is a result of 982 Mayo Clin Proc. July 2006;81(7):

11 nilotinib representing a better topographical fit for the Abl kinase pocket. However, nilotinib, like imatinib, only binds the Abl protein in its inactive conformation. Nilotinib inhibits the tyrosine kinase activity of most clinically important Bcr-Abl mutants, with the exception of T315I. 157 A phase 1/2 study of nilotinib included 106 patients with imatinib-resistant CML in all phases and 13 patients with Ph chromosome positive ALL. 170 Patients received nilotinib at dosages ranging from 50 to 1200 mg/d. In CML, hematologic response rates ranged from 44% to 89%, and cytogenetic responses ranged from 22% in lymphoid and myeloid BP to 29% in AP and 50% in CP. Among patients with Bcr-Abl mutations before nilotinib therapy, 60% had a hematologic response, and 41% had a cytogenetic response. Nilotinib dosage was escalated up to 1200 mg/d with good tolerance, and the maximum tolerated dose was estimated at 600 mg twice daily. The most common drug-related adverse events were gastrointestinal, rash, and hematologic. Importantly, greater exposure to the drug and inhibition of Bcr-Abl phosphorylation were observed with twice-daily dosing schedules compared with equivalent total doses administered on a once-daily schedule. 170 Dasatinib (BMS ). Because it is possible that inhibition of Bcr-Abl alone may not be sufficient to eradicate all CML cells, particularly the leukemic imatinibinsensitive quiescent stem cells, agents with additional inhibitory capacity against other kinases have been investigated. Since Src kinases have been implicated in CML pathogenesis and progression, dual Abl/Src inhibitors may have enhanced activity compared with imatinib. Among this new class of compounds, dasatinib has reached the furthest level of clinical development. Dasatinib is an ATPcompetitive, dual-specific Src- and Abl-kinase inhibitor with 100- to 300-fold higher potency against Bcr-Abl compared with imatinib and significant activity against c-kit (IC 50, 5 nm), platelet-derived growth factor receptor β (IC 50, 28 nm), and Hck, Fyn, Src, and Lck kinases (IC, 50 approximately 0.5 nm). 177 However, dasatinib does not inhibit the T315I mutant, even in the presence of micromolar concentrations. 157 In phase 2 studies, dasatinib was administered at 70 mg twice daily to patients with CML in all phases after imatinib failure. A CHR was achieved by 87%, 66%, 55%, and 46% of patients in CP, AP, myeloid BP, and lymphoid BP/Ph chromosome positive ALL, respectively. Among patients in CP, 44% had a CCGR, whereas 46% to 66% of patients with advanced-phase CML had MCGRs In a dose-escalating study, dasatinib rendered 2-log or greater reductions in Bcr-Abl transcripts in 43% of patients in advanced phase, and 37% of patients in CP achieved 2-log or greater reductions, including 4 patients in each group who had an MMR. 178 Overall, dasatinib is well tolerated, with myelosuppression and gastrointestinal toxic effects seen in some patients. Pleural effusions have also been reported in 10% to 15% of patients, particularly those in BP, and it is usually grade 1 or 2. Despite the impressive results achieved with dasatinib, it may not eradicate all quiescent leukemic stem cells, although it may be more effective at this level than imatinib. 149 Another dual Abl/Src kinase inhibitor termed SKI is currently being evaluated in phase 1 studies, and others, such as NS-187 (INNO406), 180 AZD0530, 181 PD166326, 182 and PD180970, 183 may soon follow. Non ATP-Competitive Bcr-Abl Inhibitors. Imatinib, nilotinib, and dasatinib are ATP-competitive inhibitors and therefore amenable to being affected in their ability to bind to the Bcr-Abl kinase by the T315I mutation, which is considered the gatekeeper of the kinase domain. Compounds that target binding sites unrelated to the ATPkinase domain may overcome this problem. ON targets the substrate-binding site of Bcr-Abl, competing with natural substrates such as Crkl but not with ATP. 184 In fact, ON causes regression of leukemia induced by intravenous injection of 32DcI3 cells that express the Bcr- Abl mutant T315I. 184 BIRB796, a p38 mitogen-activated protein kinase inhibitor, binds with excellent affinity to the Bcr-Abl T315I mutant (Kd 40 nm), although high concentrations of this compound are necessary to inhibit autophosphorylation of this mutant in Ba/F3 cells (IC 50, 1-2 µm). 159 In this regard, VX680 (MK-0457), a multikinase inhibitor that inhibits, among others, aurora A and B kinase, seems to have a more favorable profile against T315I, although remarkably less affinity for wild-type Bcr-Abl (IC 50, >10 µm). 159 Other Therapeutic Options. Other approaches are being developed for patients who develop resistance to imatinib. Farnesyl transferase inhibitors, such as lonafarnib and tipifarnib, have demonstrated activity both as single agents and in combination with imatinib This approach has rendered anecdotal responses in patients harboring the T315I mutant. Homoharringtonine is a Cephalotaxus alkaloid that represented the best therapeutic option in patients in whom interferon alfa based therapies failed before the introduction of imatinib in clinical practice. 189 Its potential as salvage therapy in imatinib-resistant CML has rekindled interest in this drug. Another avenue that has been pursued in recent years is the use of hypomethylating agents 190,191 and histone deacetylase inhibitors In a phase 2 study, decitabine administered at 15 mg/m 2, 5 days a week for 2 consecutive weeks, rendered a CHR in 34% and a CCGR in 46% of patients. 190,191 These and other agents with different targets are currently being developed in an attempt to prevent or overcome resistance to imatinib. Immune-mediated events play an important role in the suppression of the CML clone, as evidenced by a subset of Mayo Clin Proc. July 2006;81(7):

12 patients who maintained a durable CHR after discontinuation of interferon alfa therapy 195 and after allogeneic-sct due to a graft-vs-leukemia effect. 196 These observations have sparked interest in developing immunologic approaches to treating CML. One such approach is the use of vaccines to elicit specific immune responses directed toward CML-restricted tumor antigens. Several vaccines are currently being developed in clinical studies, which encompass the use of BCR-ABL junction-spanning sequences, the nonapeptide PR1 derived from proteinase 3, 200 leukocyte-derived HSP70-peptide complexes, 201 and granulocyte-macrophage colony-stimulating factor secreting vaccines. 202 The Bcr-Abl breakpoint fusion peptide vaccine has been already tested in phase 2 clinical studies. 198,199 Bocchia et al 199 have reported on 16 patients with stable residual disease after more than 12 months of imatinib therapy (n=10) or 24 months of interferon alfa therapy (n=6) who received 6 vaccinations with a peptide vaccine derived from the sequence p210-b3a2. Five of 9 patients taking imatinib obtained a CCGR after vaccination, and 3 had undetectable levels of b3a2 transcripts by RT-PCR. Among the patients treated with interferon alfa, 2 achieved a CCGR, and 3 had improvement in the percentage of Ph chromosome positive metaphases. Overall, these data suggest that this peptide vaccine may have a role in the management of patients with CML and minimal residual disease. SUMMARY Consensus exists that imatinib therapy is the standard approach to the treatment of CML, and this modality will be measured in the future against all new therapies. The recent addition of the highly potent TKIs nilotinib and dasatinib has further improved the armamentarium against CML but also posed new challenges. First, the role of these new compounds in modern algorithms of CML therapy is still unknown and must be defined. Despite having shown impressive response rates in patients after imatinib failure or intolerance, the duration of these responses will be determined with longer follow-up. Their role in frontline therapy for CML will also have to be defined. Second, as our resources for controlling CML improve, the refinement in molecular monitoring must improve in parallel. In this regard, the lack of consistency among different laboratories in BCR-ABL transcript results by current PCR technologies is still an ongoing problem. Future improvements in molecular techniques and their standardization by using a laboratory-specific conversion factor will be crucial to further our understanding of the dynamics of molecular response to TKIs, providing a uniform method and definition of MMR and defining the concept of molecular relapse. Other challenges, such as defining the best treatment for patients who develop the Bcr-Abl T315I mutant, understanding the mechanism of resistance of patients without detectable mutations, the emergence of new mechanisms of resistance such as new mutations to the new TKI and other agents, developing novel strategies for the management of minimal residual disease, and delineating the current role of SCT, will be the subject of arduous investigation in future years. Despite all these uncertainties, the treatment prospects of patients with CML have never been brighter. REFERENCES 1. Abramson S, Miller RG, Phillips RA. The identification in adult bone marrow of pluripotent and restricted stem cells of the myeloid and lymphoid systems. J Exp Med. 1977;145: Bennett J. Case of hypertrophy of the spleen and liver in which death took place from suppuration of the blood. Edinb Med Surg J. 1845;64: Dameshek W. Some speculations on the myeloproliferative syndromes. Blood. 1951;6: Nowell PC, Hungerford DA. A minute chromosome in human chronic granulocytic leukemia. Science. 1960;132: Rowley JD. Letter: A new consistent chromosomal abnormality in chronic myelogenous leukaemia identified by quinacrine fluorescence and Giemsa staining. Nature. 1973;243: Bartram CR, de Klein A, Hagemeijer A, et al. Translocation of c-ab1 oncogene correlates with the presence of a Philadelphia chromosome in chronic myelocytic leukaemia. Nature. 1983;306: Groffen J, Stephenson JR, Heisterkamp N, de Klein A, Bartram CR, Grosveld G. Philadelphia chromosomal breakpoints are clustered within a limited region, bcr, on chromosome 22. Cell. 1984;36: Jemal A, Tiwari RC, Murray T, et al. Cancer statistics, CA Cancer J Clin. 2004;54: Deininger MW, Goldman JM, Melo JV. The molecular biology of chronic myeloid leukemia. Blood. 2000;96: Bizzozero OJ Jr, Johnson KG, Ciocco A, Kawasaki S, Toyoda S. Radiation-related leukemia in Hiroshima and Nagasaki : II. Ann Intern Med. 1967;66: Kantarjian HM, Keating MJ, Smith TL, Talpaz M, McCredie KB. Proposal for a simple synthesis prognostic staging system in chronic myelogenous leukemia. Am J Med. 1990;88: Speck B, Bortin MM, Champlin R, et al. Allogeneic bone-marrow transplantation for chronic myelogenous leukaemia. Lancet. 1984;1: Vardiman JW, Harris NL, Brunning RD. The World Health Organization (WHO) classification of the myeloid neoplasms. Blood. 2002;100: Kantarjian HM, Smith TL, McCredie KB, et al. Chronic myelogenous leukemia: a multivariate analysis of the associations of patient characteristics and therapy with survival. Blood. 1985;66: Sokal JE, Baccarani M, Russo D, Tura S. Staging and prognosis in chronic myelogenous leukemia. Semin Hematol. 1988;25: Sokal JE, Baccarani M, Tura S, et al. Prognostic discrimination among younger patients with chronic granulocytic leukemia: relevance to bone marrow transplantation. Blood. 1985;66: Kantarjian HM, Dixon D, Keating MJ, et al. Characteristics of accelerated disease in chronic myelogenous leukemia. Cancer. 1988;61: Cortes JE, Talpaz M, O Brien S, et al. Staging of chronic myeloid leukemia in the imatinib era: an evaluation of the World Health Organization proposal. Cancer. 2006;106: Cortes J, Kantarjian H. Advanced-phase chronic myeloid leukemia. Semin Hematol. 2003;40: Karanas A, Silver RT. Characteristics of the terminal phase of chronic granulocytic leukemia. Blood. 1968;32: Griesshammer M, Heinze B, Hellmann A, et al. Chronic myelogenous leukemia in blast crisis: retrospective analysis of prognostic factors in 90 patients. Ann Hematol. 1996;73: Kantarjian HM, Keating MJ, Talpaz M, et al. Chronic myelogenous leukemia in blast crisis: analysis of 242 patients. Am J Med. 1987;83: Cortes JE, Talpaz M, Kantarjian H. Chronic myelogenous leukemia: a review. Am J Med. 1996;100: Cramer E, Auclair C, Hakim J, et al. Metabolic activity of phagocytosing granulocytes in chronic granulocytic leukemia: ultrastructural observation of a degranulation defect. Blood. 1977;50: Mayo Clin Proc. July 2006;81(7):

13 25. Denburg JA, Wilson WE, Bienenstock J. Basophil production in myeloproliferative disorders: increases during acute blastic transformation of chronic myeloid leukemia. Blood. 1982;60: Silver RT. Morphology Of The Blood And Marrow In Clinical Practice. New York, NY: Grune & Stratton; 1970: Strife A, Clarkson B. Biology of chronic myelogenous leukemia: is discordant maturation the primary defect? Semin Hematol. 1988;25: Gordon MY, Dowding CR, Riley GP, Goldman JM, Greaves MF. Altered adhesive interactions with marrow stroma of haematopoietic progenitor cells in chronic myeloid leukaemia. Nature. 1987;328: Dosik H, Rosner F, Sawitsky A. Acquired lipidosis: Gaucher-like cells and blue cells in chronic granulocytic leukemia. Semin Hematol. 1972;9: Castro-Malaspina H, Moore MA. Pathophysiological mechanisms operating in the development of myelofibrosis: role of megakaryocytes. Nouv Rev Fr Hematol. 1982;24: Aguayo A, Kantarjian H, Manshouri T, et al. Angiogenesis in acute and chronic leukemias and myelodysplastic syndromes. Blood. 2000;96: Derderian PM, Kantarjian HM, Talpaz M, et al. Chronic myelogenous leukemia in the lymphoid blastic phase: characteristics, treatment response, and prognosis. Am J Med. 1993;94: Bain B, Catovsky D, O Brien M, Spiers AS, Richards GH. Megakaryoblastic transformation of chronic granulocytic leukaemia. An electron microscopy and cytochemial study. J Clin Pathol. 1977;30: Rosenthal S, Cancellos GP, Gralnick HP. Erythroblastic transformation of chronic granulocytic leukemia. Am J Med. 1977;63: Soler J, O Brien M, de Castro JT, et al. Blast crisis of chronic granulocytic leukemia with mast cell and basophilic precursors. Am J Clin Pathol. 1985;83: Sokal JE, Cox EB, Baccarani M, et al. Prognostic discrimination in good-risk chronic granulocytic leukemia. Blood. 1984;63: Silver RT, Peterson BL, Szatrowski TP, et al. Treatment of the chronic phase of chronic myeloid leukemia with an intermittent schedule of recombinant interferon alfa-2b and cytarabine: results from CALGB study Leuk Lymphoma. 2003;44: Quintas-Cardama A, Kantarjian H, Talpaz M, et al. Imatinib mesylate therapy may overcome the poor prognostic significance of deletions of derivative chromosome 9 in patients with chronic myelogenous leukemia. Blood. 2005;105: Hasford J, Pfirrmann M, Hehlmann R, et al, Writing Committee for the Collaborative CML Prognostic Factors Project Group. A new prognostic score for survival of patients with chronic myeloid leukemia treated with interferon alfa. J Natl Cancer Inst. 1998;90: Gratwohl A, Hermans J, Niederwieser D, et al, Chronic Leukemia Working Party of the European Group for Bone Marrow Transplantation. Bone marrow transplantation for chronic myeloid leukemia: long-term results. Bone Marrow Transplant. 1993;12: Kurzrock R, Gutterman JU, Talpaz M. The molecular genetics of Philadelphia chromosome-positive leukemias. N Engl J Med. 1988;319: Huret JL. Complex translocations, simple variant translocations and Phnegative cases in chronic myelogenous leukaemia. Hum Genet. 1990;85: De Braekeleer M. Variant Philadelphia translocations in chronic myeloid leukemia. Cytogenet Cell Genet. 1987;44: Albano F, Specchia G, Pannunzio A, et al. Variant t(9;22) translocation may identify a subgroup of chronic myeloid leukemia patients with poor prognosis [abstract]. Blood. 2001;98:321a. 45. El-Zimaity MM, Kantarjian H, Talpaz M, et al. Results of imatinib mesylate therapy in chronic myelogenous leukaemia with variant Philadelphia chromosome. Br J Haematol. 2004;125: Shtalrid M, Talpaz M, Blick M, et al. Philadelphia-negative chronic myelogenous leukemia with breakpoint cluster region rearrangement: molecular analysis, clinical characteristics, and response to therapy. J Clin Oncol. 1988;6: Kurzrock R, Kantarjian HM, Shtalrid M, Gutterman JU, Talpaz M. Philadelphia chromosome-negative chronic myelogenous leukemia without breakpoint cluster region rearrangement: a chronic myeloid leukemia with a distinct clinical course. Blood. 1990;75: Jennings BA, Mills KI. c-myc locus amplification and the acquisition of trisomy 8 in the evolution of chronic myeloid leukaemia. Leuk Res. 1998; 22: Calabretta B, Perrotti D. The biology of CML blast crisis. Blood. 2004; 103: Gaiger A, Henn T, Horth E, et al. Increase of bcr-abl chimeric mrna expression in tumor cells of patients with chronic myeloid leukemia precedes disease progression. Blood. 1995;86: Mitelman F, Levan G, Nilsson PG, Brandt L. Non-random karyotypic evolution in chronic myeloid leukemia. Int J Cancer. 1976;18: Lawler SD, O Malley F, Lobb DS. Chromosome banding studies in Philadelphia chromosome positive myeloid leukaemia. Scand J Haematol. 1976;17: Feinstein E, Cimino G, Gale RP, et al. p53 in chronic myelogenous leukemia in acute phase. Proc Natl Acad Sci U S A. 1991;88: Sill H, Goldman JM, Cross NC. Homozygous deletions of the p16 tumor-suppressor gene are associated with lymphoid transformation of chronic myeloid leukemia. Blood. 1995;85: Towatari M, Adachi K, Kato H, Saito H. Absence of the human retinoblastoma gene product in the megakaryoblastic crisis of chronic myelogenous leukemia. Blood. 1991;78: Ogawa S, Mitani K, Kurokawa M, et al. Abnormal expression of Evi-1 gene in human leukemias. Hum Cell. 1996;9: Ahuja H, Bar-Eli M, Arlin Z, et al. The spectrum of molecular alterations in the evolution of chronic myelocytic leukemia. J Clin Invest. 1991; 87: Jamieson CH, Ailles LE, Dylla SJ, et al. Granulocyte-macrophage progenitors as candidate leukemic stem cells in blast-crisis CML. N Engl J Med. 2004;351: Zion M, Ben-Yehuda D, Avraham A, et al. Progressive de novo DNA methylation at the bcr-abl locus in the course of chronic myelogenous leukemia. Proc Natl Acad Sci U S A. 1994;91: Issa JP, Kantarjian H, Mohan A, et al. Methylation of the ABL1 promoter in chronic myelogenous leukemia: lack of prognostic significance. Blood. 1999;93: Asimakopoulos FA, Shteper PJ, Krichevsky S, et al. ABL1 methylation is a distinct molecular event associated with clonal evolution of chronic myeloid leukemia. Blood. 1999;94: Roman-Gomez J, Castillejo JA, Jimenez A, et al. Cadherin-13, a mediator of calcium-dependent cell-cell adhesion, is silenced by methylation in chronic myeloid leukemia and correlates with pretreatment risk profile and cytogenetic response to interferon alfa. J Clin Oncol. 2003;21: Loriaux M, Deininger M. Clonal cytogenetic abnormalities in Philadelphia chromosome negative cells in chronic myeloid leukemia patients treated with imatinib. Leuk Lymphoma. 2004;45: Fayad L, Kantarjian H, O Brien S, et al. Emergence of new clonal abnormalities following interferon-alpha induced complete cytogenetic response in patients with chronic myeloid leukemia: report of three cases. Leukemia. 1997;11: Medina J, Kantarjian H, Talpaz M, et al. Chromosomal abnormalities in Philadelphia chromosome-negative metaphases appearing during imatinib mesylate therapy in patients with Philadelphia chromosome-positive chronic myelogenous leukemia in chronic phase. Cancer. 2003;98: Bumm T, Muller C, Al-Ali HK, et al. Emergence of clonal cytogenetic abnormalities in Ph-cells in some CML patients in cytogenetic remission to imatinib but restoration of polyclonal hematopoiesis in the majority. Blood. 2003;101: Abelson HT, Rabstein LS. Lymphosarcoma: virus-induced thymicindependent disease in mice. Cancer Res. 1970;30: Laneuville P. Abl tyrosine protein kinase. Semin Immunol. 1995;7: Bernards A, Rubin CM, Westbrook CA, Paskind M, Baltimore D. The first intron in the human c-abl gene is at least 200 kilobases long and is a target for translocations in chronic myelogenous leukemia. Mol Cell Biol. 1987;7: Heisterkamp N, Jenster G, ten Hoeve J, Zovich D, Pattengale PK, Groffen J. Acute leukaemia in bcr/abl transgenic mice. Nature. 1990;344: Melo JV. The diversity of BCR-ABL fusion proteins and their relationship to leukemia phenotype. Blood. 1996;88: Faderl S, Talpaz M, Estrov Z, O Brien S, Kurzrock R, Kantarjian HM. The biology of chronic myeloid leukemia. N Engl J Med. 1999;341: Sawyers CL. Chronic myeloid leukemia. N Engl J Med. 1999;340: Ravandi F, Cortes J, Albitar M, et al. Chronic myelogenous leukaemia with p185(bcr/abl) expression: characteristics and clinical significance. Br J Haematol. 1999;107: Pane F, Frigeri F, Sindona M, et al. Neutrophilic-chronic myeloid leukemia: a distinct disease with a specific molecular marker (BCR/ABL with C3/ A2 junction). Blood. 1996;88: Lugo TG, Pendergast AM, Muller AJ, Witte ON. Tyrosine kinase activity and transformation potency of bcr-abl oncogene products. Science. 1990;247: Bose S, Deininger M, Gora-Tybor J, Goldman JM, Melo JV. The presence of typical and atypical BCR-ABL fusion genes in leukocytes of Mayo Clin Proc. July 2006;81(7):

14 normal individuals: biologic significance and implications for the assessment of minimal residual disease. Blood. 1998;92: Biernaux C, Sels A, Huez G, Stryckmans P. Very low level of major BCR-ABL expression in blood of some healthy individuals. Bone Marrow Transplant. 1996;17(suppl 3):S45-S Angel P, Karin M. The role of Jun, Fos and the AP-1 complex in cellproliferation and transformation. Biochim Biophys Acta. 1991;1072: Liebermann DA, Gregory B, Hoffman B. AP-1 (Fos/Jun) transcription factors in hematopoietic differentiation and apoptosis. Int J Oncol. 1998;12: Passegue E, Jochum W, Schorpp-Kistner M, Mohle-Steinlein U, Wagner EF. Chronic myeloid leukemia with increased granulocyte progenitors in mice lacking junb expression in the myeloid lineage. Cell. 2001;104: Ramaraj P, Singh H, Niu N, et al. Effect of mutational inactivation of tyrosine kinase activity on BCR/ABL-induced abnormalities in cell growth and adhesion in human hematopoietic progenitors. Cancer Res. 2004;64: Zhao RC, Jiang Y, Verfaillie CM. A model of human p210(bcr/abl)- mediated chronic myelogenous leukemia by transduction of primary normal human CD34(+) cells with a BCR/ABL-containing retroviral vector. Blood. 2001;97: Daley GQ, Van Etten RA, Baltimore D. Induction of chronic myelogenous leukemia in mice by the P210bcr/abl gene of the Philadelphia chromosome. Science. 1990;247: Kelliher MA, McLaughlin J, Witte ON, Rosenberg N. Induction of a chronic myelogenous leukemia-like syndrome in mice with v-abl and BCR/ ABL. Proc Natl Acad Sci U S A. 1990;87: Pendergast AM, Gishizky ML, Havlik MH, Witte ON. SH1 domain autophosphorylation of P210 BCR/ABL is required for transformation but not growth factor independence. Mol Cell Biol. 1993;13: Zhang X, Subrahmanyam R, Wong R, Gross AW, Ren R. The NH(2)- terminal coiled-coil domain and tyrosine 177 play important roles in induction of a myeloproliferative disease in mice by Bcr-Abl. Mol Cell Biol. 2001;21: Ren R. Mechanisms of BCR-ABL in the pathogenesis of chronic myelogenous leukaemia. Nat Rev Cancer. 2005;5: Pendergast AM, Quilliam LA, Cripe LD, et al. BCR-ABL-induced oncogenesis is mediated by direct interaction with the SH2 domain of the GRB-2 adaptor protein. Cell. 1993;75: Hu Y, Liu Y, Pelletier S, et al. Requirement of Src kinases Lyn, Hck and Fgr for BCR-ABL1-induced B-lymphoblastic leukemia but not chronic myeloid leukemia. Nat Genet. 2004;36: Bhatia R, Holtz M, Niu N, et al. Persistence of malignant hematopoietic progenitors in chronic myelogenous leukemia patients in complete cytogenetic remission following imatinib mesylate treatment. Blood. 2003;101: Donato NJ, Wu JY, Stapley J, et al. BCR-ABL independence and LYN kinase overexpression in chronic myelogenous leukemia cells selected for resistance to STI571. Blood. 2003;101: Kerkhoff E, Rapp UR. Cell cycle targets of Ras/Raf signalling. Oncogene. 1998;17: Nosaka T, Kawashima T, Misawa K, Ikuta K, Mui AL, Kitamura T. STAT5 as a molecular regulator of proliferation, differentiation and apoptosis in hematopoietic cells. Embo J. 1999;18: Sonoyama J, Matsumura I, Ezoe S, et al. Functional cooperation among Ras, STAT5, and phosphatidylinositol 3-kinase is required for full oncogenic activities of BCR/ABL in K562 cells. J Biol Chem. 2002;277: Neviani P, Santhanam R, Trotta R, et al. The tumor suppressor PP2A is functionally inactivated in blast crisis CML through the inhibitory activity of the BCR/ABL-regulated SET protein. Cancer Cell. 2005;8: Janssens V, Goris J. Protein phosphatase 2A: a highly regulated family of serine/threonine phosphatases implicated in cell growth and signalling. Biochem J. 2001;353(pt 3): Talpaz M, Mavligit G, Keating M, Walters RS, Gutterman JU. Human leukocyte interferon to control thrombocytosis in chronic myelogenous leukemia. Ann Intern Med. 1983;99: Talpaz M, Kantarjian HM, McCredie K, Trujillo JM, Keating MJ, Gutterman JU. Hematologic remission and cytogenetic improvement induced by recombinant human interferon alpha A in chronic myelogenous leukemia. N Engl J Med. 1986;314: Kantarjian HM, Smith TL, O Brien S, Beran M, Pierce S, Talpaz M, The Leukemia Service. Prolonged survival in chronic myelogenous leukemia after cytogenetic response to interferon-alpha therapy. Ann Intern Med. 1995; 122: O Brien S, Kantarjian H, Koller C, et al. Sequential homoharringtonine and interferon-alpha in the treatment of early chronic phase chronic myelogenous leukemia. Blood. 1999;93: O Brien S, Talpaz M, Cortes J, et al. Simultaneous homoharringtonine and interferon-alpha in the treatment of patients with chronic-phase chronic myelogenous leukemia. Cancer. 2002;94: Baccarani M, Rosti G, de Vivo A, et al. A randomized study of interferon-alpha versus interferon-alpha and low-dose arabinosyl cytosine in chronic myeloid leukemia. Blood. 2002;99: Kantarjian HM, O Brien S, Smith TL, et al. Treatment of Philadelphia chromosome-positive early chronic phase chronic myelogenous leukemia with daily doses of interferon alpha and low-dose cytarabine. J Clin Oncol. 1999;17: Guilhot F, Chastang C, Michallet M, et al, French Chronic Myeloid Leukemia Study Group. Interferon alfa-2b combined with cytarabine versus interferon alone in chronic myelogenous leukemia. N Engl J Med. 1997;337: Kantarjian HM, O Brien S, Cortes JE, et al. Complete cytogenetic and molecular responses to interferon-alpha-based therapy for chronic myelogenous leukemia are associated with excellent long-term prognosis. Cancer. 2003;97: Hochhaus A, Reiter A, Saussele S, et al, German CML Study Group and the UK MRC CML Study Group. Molecular heterogeneity in complete cytogenetic responders after interferon-alpha therapy for chronic myelogenous leukemia: low levels of minimal residual disease are associated with continuing remission. Blood. 2000;95: Molldrem JJ, Lee PP, Wang C, et al. Evidence that specific T lymphocytes may participate in the elimination of chronic myelogenous leukemia. Nat Med. 2000;6: Morton AJ, Gooley T, Hansen JA, et al. Association between pretransplant interferon-alpha and outcome after unrelated donor marrow transplantation for chronic myelogenous leukemia in chronic phase. Blood. 1998;92: Giralt SA, Kantarjian HM, Talpaz M, et al. Effect of prior interferon alfa therapy on the outcome of allogeneic bone marrow transplantation for chronic myelogenous leukemia. J Clin Oncol. 1993;11: Giralt S, Szydlo R, Goldman JM, et al. Effect of short-term interferon therapy on the outcome of subsequent HLA-identical sibling bone marrow transplantation for chronic myelogenous leukemia: an analysis from the international bone marrow transplant registry. Blood. 2000;95: Hehlmann R, Hochhaus A, Kolb HJ, et al. Interferon-alpha before allogeneic bone marrow transplantation in chronic myelogenous leukemia does not affect outcome adversely, provided it is discontinued at least 90 days before the procedure. Blood. 1999;94: Lee SJ, Klein JP, Anasetti C, et al. The effect of pretransplant interferon therapy on the outcome of unrelated donor hematopoietic stem cell transplantation for patients with chronic myelogenous leukemia in first chronic phase. Blood. 2001;98: Holowiecki J, Kruzel T, Wojnar J, et al. Allogeneic stem cell transplantation from unrelated and related donors is effective in CML Ph+ and ALL Ph+ patients pretreated with imatinib [abstract]. Blood. 2003;102(pt 2):436b Prejzner W, Zaucha JM, Szatkowski D, et al. Imatinib therapy prior to myeloablative allogeneic stem cell transplantation does not increase acute transplant related toxicity [abstract]. Blood. 2003;102(pt 1):911a Hansen JA, Gooley TA, Martin PJ, et al. Bone marrow transplants from unrelated donors for patients with chronic myeloid leukemia. N Engl J Med. 1998;338: Baker KS, Gurney JG, Ness KK, et al. Late effects in survivors of chronic myeloid leukemia treated with hematopoietic cell transplantation: results from the Bone Marrow Transplant Survivor Study. Blood. 2004;104: Kiss TL, Abdolell M, Jamal N, Minden MD, Lipton JH, Messner HA. Long-term medical outcomes and quality-of-life assessment of patients with chronic myeloid leukemia followed at least 10 years after allogeneic bone marrow transplantation. J Clin Oncol. 2002;20: Radich JP, Gooley T, Bensinger W, et al. HLA-matched related hematopoietic cell transplantation for chronic-phase CML using a targeted busulfan and cyclophosphamide preparative regimen. Blood. 2003;102: Weisdorf DJ, Anasetti C, Antin JH, et al. Allogeneic bone marrow transplantation for chronic myelogenous leukemia: comparative analysis of unrelated versus matched sibling donor transplantation. Blood. 2002;99: Or R, Shapira MY, Resnick I, et al. Nonmyeloablative allogeneic stem cell transplantation for the treatment of chronic myeloid leukemia in first chronic phase. Blood. 2003;101: Crawley C, Szydlo R, Lalancette M, et al. Outcomes of reduced-intensity transplantation for chronic myeloid leukemia: an analysis of prognostic factors from the Chronic Leukemia Working Party of the EBMT. Blood. 2005;106: Epub 2005 Jul Mayo Clin Proc. July 2006;81(7):

15 123. Radich JP, Gehly G, Gooley T, et al. Polymerase chain reaction detection of the BCR-ABL fusion transcript after allogeneic marrow transplantation for chronic myeloid leukemia: results and implications in 346 patients. Blood. 1995;85: Olavarria E, Craddock C, Dazzi F, et al. Imatinib mesylate (STI571) in the treatment of relapse of chronic myeloid leukemia after allogeneic stem cell transplantation. Blood. 2002;99: Druker BJ, Tamura S, Buchdunger E, et al. Effects of a selective inhibitor of the Abl tyrosine kinase on the growth of Bcr-Abl positive cells. Nat Med. 1996;2: Beran M, Cao X, Estrov Z, et al. Selective inhibition of cell proliferation and BCR-ABL phosphorylation in acute lymphoblastic leukemia cells expressing Mr 190,000 BCR-ABL protein by a tyrosine kinase inhibitor (CGP-57148). Clin Cancer Res. 1998;4: Druker BJ, Talpaz M, Resta DJ, et al. Efficacy and safety of a specific inhibitor of the BCR-ABL tyrosine kinase in chronic myeloid leukemia. N Engl J Med. 2001;344: Kantarjian H, Sawyers C, Hochhaus A, et al. Hematologic and cytogenetic responses to imatinib mesylate in chronic myelogenous leukemia. N Engl J Med. 2002;346: Kantarjian HM, Cortes JE, O Brien S, et al. Long-term survival benefit and improved complete cytogenetic and molecular response rates with imatinib mesylate in Philadelphia chromosome-positive chronic-phase chronic myeloid leukemia after failure of interferon-alpha. Blood. 2004;104: O Brien SG, Guilhot F, Larson RA, et al. Imatinib compared with interferon and low-dose cytarabine for newly diagnosed chronic-phase chronic myeloid leukemia. N Engl J Med. 2003;348: Hahn EA, Glendenning GA, Sorensen MV, et al. Quality of life in patients with newly diagnosed chronic phase chronic myeloid leukemia on imatinib versus interferon alfa plus low-dose cytarabine: results from the IRIS Study. J Clin Oncol. 2003;21: Simonsson B, the IRIS (International Randomized IFN vs ST1571) Study Group. Beneficial effects of cytogenetic and molecular response on long-term outcome in patients with newly diagnosed chronic myeloid leukemia in chronic phase (CML-CP) treated with imatinib (IM): update from the IRIS study [abstract]. Blood. 2005;106:52a Colombat M, Fort MP, Chollet C, et al. Molecular remission in chronic myeloid leukemia patients with sustained complete cytogenetic remission after imatinib mesylate treatment. Haematologica. 2006;91: Goldman JM, Hughes T, Radich J, et al. Continuing reduction in level of residual disease after 4 years in patients with CML in chronic phase responding to first-line imatinib (IM) in the IRIS study [abstract]. Blood. 2005; 106:51a Kantarjian H, O Brien S, Cortes J, et al. Analysis of the impact of imatinib mesylate therapy on the prognosis of patients with Philadelphia chromosome-positive chronic myelogenous leukemia treated with interferonalpha regimens for early chronic phase. Cancer. 2003;98: Roy L, Guilhot J, Krahnke T, et al. Survival advantage from imatinib compared to the combination interferon-{alpha} plus cytarabine in chronic phase CML: historical comparison between two phase III trials. Blood. Epub 2006 Apr Kantarjian H, Talpaz M, O Brien S, et al. High-dose imatinib mesylate therapy in newly diagnosed Philadelphia chromosome-positive chronic phase chronic myeloid leukemia. Blood. 2004;103: Hughes TP, Branford S, Matthews J, et al. Trial of higher dose imatinib with selective intensification in newly diagnosed CML patients in the chronic phase [abstract]. Blood. 2003;102(Pt 1):31a Cortes J, Giles F, Salvado A, et al. High-dose (HD) imatinib in patients (pts) with previously untreated chronic myeloid leukemia (CML) in early chronic phase (CP): preliminary results of a multicenter community based trial [abstract]. J Clin Oncol. 2005;23(suppl):564s Rosti G, Martinelli G, Castagnetti F, et al. Imatinib 800 mg: preliminary results of a phase II trial of the GIMEMA CML working party in intermediate sokal risk patients and status-of-the-art of an ongoing multinational, prospective randomized trial of imatinib standard dose (400 mg daily) vs high dose (800 mg daily) in high sokal risk patients [abstract]. Blood. 2005;106:320a Cortes J, Giles F, O Brien S, et al. Result of high-dose imatinib mesylate in patients with Philadelphia chromosome-positive chronic myeloid leukemia after failure of interferon-alpha. Blood. 2003;102: Cortes J, Talpaz M, O Brien S, et al. Molecular responses in patients with chronic myelogenous leukemia in chronic phase treated with imatinib mesylate. Clin Cancer Res. 2005;11: Hughes TP, Branford S, Reynolds J, et al. Maintenance of imatinib dose intensity in the first six months of therapy for newly diagnosed patients with CML is predictive of molecular response, independent of the ability to increase dose at a later point [abstract]. Blood. 2005;106:51a Cortes J, O Brien S, Kantarjian H. Discontinuation of imatinib therapy after achieving a molecular response. Blood. 2004;104: Mauro MJ, Druker BJ, Maziarz RT. Divergent clinical outcome in two CML patients who discontinued imatinib therapy after achieving a molecular remission. Leuk Res. 2004;28(suppl 1):S71-S Ghanima W, Kahrs J, Dahl TG, 3rd, Tjonnfjord GE. Sustained cytogenetic response after discontinuation of imatinib mesylate in a patient with chronic myeloid leukaemia. Eur J Haematol. 2004;72: Rousselot P, Huguet F, Cayuela JM, et al. Imatinib mesylate discontinuation in patients with chronic myelogenous leukaemia in complete molecular remission for more than two years [abstract]. Blood. 2005;106:321a Graham SM, Jorgensen HG, Allan E, et al. Primitive, quiescent, Philadelphia-positive stem cells from patients with chronic myeloid leukemia are insensitive to STI571 in vitro. Blood. 2002;99: Copland M. Hamilton A, Baird JW, et al. Dasatinib (BMS ) has increased activity against Bcr-Abl compared to imatinib in primary CML cells in vitro, but does not eradicate quiescent CML stem cells [abstract]. Blood. 2005;106:205a Chu S, Xu H, Shah NP, et al. Detection of BCR-ABL kinase mutations in CD34+ cells from chronic myelogenous leukemia patients in complete cytogenetic remission on imatinib mesylate treatment. Blood. 2005;105: Jiang X, Zhao Y, Chan P, et al. Quantitative real-time RT-PCR analysis shows BCR-ABL expression progressively decreases as primitive leukemic cells from patients with chronic myeloid leukemia (CML) differentiate in vivo [abstract]. Exp Hematol. 2003;31: Hughes T, Kaeda J, Branford S, et al. Molecular responses to imatinib (STI571) or interferon + Ara-C as initial therapy for CML: results in the IRIS study [abstract]. Blood. 2002;100:93a Cortes J, O Brien S, Talpaz M, et al. Clinical significance of molecular response in chronic myeloid leukemia (CML) after imatinib mesylate (Gleevec) therapy: low levels of residual disease predict for response duration [abstract]. Blood. 2003;102(Pt 1):416a Talpaz M, Kantarjian H, Kurzrock R, Trujillo JM, Gutterman JU. Interferon-alpha produces sustained cytogenetic responses in chronic myelogenous leukemia. Philadelphia chromosome-positive patients. Ann Intern Med. 1991;114: Hughes TP, Deininger MW, Hochhaus A, et al. Monitoring CML patients responding to treatment with tyrosine kinase inhibitors: review and recommendations for harmonizing current methodology for detecting BCR- ABL transcripts and kinase domain mutations and for expressing results. Blood. Epub 2006 Mar Hochhaus A, La Rosee P. Imatinib therapy in chronic myelogenous leukemia: strategies to avoid and overcome resistance. Leukemia. 2004;18: O Hare T, Walters DK, Stoffregen EP, et al. In vitro activity of Bcr-Abl inhibitors AMN107 and BMS against clinically relevant imatinibresistant Abl kinase domain mutants. Cancer Res. 2005;65: Deininger M, Buchdunger E, Druker BJ. The development of imatinib as a therapeutic agent for chronic myeloid leukemia. Blood. 2005;105: Carter TA, Wodicka LM, Shah NP, et al. Inhibition of drug-resistant mutants of ABL, KIT, and EGF receptor kinases. Proc Natl Acad Sci U S A. 2005;102: Cowan-Jacob SW, Guez V, Fendrich G, et al. Imatinib (STI571) resistance in chronic myelogenous leukemia: molecular basis of the underlying mechanisms and potential strategies for treatment. Mini Rev Med Chem. 2004;4: Branford S, Rudzki Z, Walsh S, et al. Detection of BCR-ABL mutations in patients with CML treated with imatinib is virtually always accompanied by clinical resistance, and mutations in the ATP phosphate-binding loop (P-loop) are associated with a poor prognosis. Blood. 2003;102: Hochhaus A, Kreil S, Corbin A, et al. Roots of clinical resistance to STI- 571 cancer therapy. Science. 2001;293: Soverini S, Martinelli G, Rosti G, et al. ABL mutations in late chronic phase chronic myeloid leukemia patients with up-front cytogenetic resistance to imatinib are associated with a greater likelihood of progression to blast crisis and shorter survival: a study by the GIMEMA Working Party on Chronic Myeloid Leukemia. J Clin Oncol. 2005;23: Jabbour E, Kantarjian H, Jones D, et al. Long-term incidence and outcome of BCR-ABL mutations in patients (pts) with chronic myeloid leukemia (CML) treated with imatinib mesylate: P-loop mutations are not associated with worse outcome [abstract]. Blood. 2004;104:288a Jabbour E, Kantarjian H, Talpaz M, et al. Outcome of salvage therapy in patients (pts) with chronic myeloid leukemia (CML) who failed imatinib after developing BCR-ABL kinase mutation [abstract]. Blood. 2005;106: 318a. Mayo Clin Proc. July 2006;81(7):

16 166. Pricl S, Fermeglia M, Ferrone M, Tamborini E. T315I-mutated Bcr-Abl in chronic myeloid leukemia and imatinib: insights from a computational study. Mol Cancer Ther. 2005;4: Tanis KQ, Veach D, Duewel HS, Bornmann WG, Koleske AJ. Two distinct phosphorylation pathways have additive effects on Abl family kinase activation. Mol Cell Biol. 2003;23: Leguay T, Desplat V, Marit G, Mahon FX. D276G mutation is associated with a poor prognosis in imatinib mesylate-resistant chronic myeloid leukemia patients [letter]. Leukemia. 2005;19: ; author reply Donato NJ, Wu JY, Stapley J, et al. Imatinib mesylate resistance through BCR-ABL independence in chronic myelogenous leukemia. Cancer Res. 2004;64: Kantarjian H, Ottmann O, Cortes J, et al. AMN107, a novel aminopyrimidine inhibitor of Bcr-Abl, has significant activity in imatinib-resistant bcr-abl positive chronic myeloid leukemia (CML) [abstract]. J Clin Oncol. 2005;23(suppl):195s Sawyers CL, Shah NP, Kantarjian HM, et al. A phase I study of BMS in patients with imatinib-resistant and intolerant accelerated and blast phase chronic myeloid leukemia (CML): results from CA [abstract]. J Clin Oncol. 2005;23(suppl):565s Talpaz M, Kantarjian H, Paquette R, et al. A phase I study of BMS in patients with imatinib-resistant and intolerant chronic phase chronic myeloid leukemia (CML): results from CA [abstract]. J Clin Oncol. 2005;23(suppl):564s Hochhaus A, Baccarani M, Sawhers C, et al. Efficacy of dasatinib in patients with chronic phase Philadelphia chromosome-positive CML resistant or intolerant to imatinib: first results of the CA START-C phase II study [abstract]. Blood. 2005;106:17a Guilhot F, Apperley JF, Shah N, et al. A phase II study of dasatinib in patients with accelerated phase chronic myeloid leukemia (CML) who are resistant or intolerant to imatinib: first results of the CA START-A study [abstract]. Blood. 2005;106:16a Talpaz M, Rousselot P, Kim DW, et al. A phase II study of dasatinib in patients with chronic myeloid leukemia (CML) in myeloid blast crisis who are resistant or intolerant to imatinib: first results of the CA START-B study [abstract]. Blood. 2005;106:16a Ottmann OG, Martinelli G, Dombret H, et al. A phase II study of dasatinib in patients with chronic myeloid leukemia (CML) in lymphoid blast crisis or Philadelphia-chromosome positive acute lymphoblastic leukemia (Ph+ ALL) who are resistant or intolerant to imatinib: the START-L CA study [abstract]. Blood. 2005;106:17a Lombardo LJ, Lee FY, Chen P, et al. Discovery of N-(2-chloro-6- methyl-phenyl)-2-(6-(4-(2-hydroxyethyl)-piperazin-1-yl)-2-methylpyrimidin- 4- ylamino)thiazole-5-carboxamide (BMS ), a dual Src/Abl kinase inhibitor with potent antitumor activity in preclinical assays. J Med Chem. 2004;47: Shah NP, Nicoll JM, Branford S, et al. Molecular analysis of dasatinib resistance mechanisms in CML patients identified novel BCR-ABL mutations predicted to retain sensitivity to imatinib: rationale for combination tyrosine kinase inhibitor therapy [abstract]. Blood. 2005;106:318a Golas JM, Arndt K, Etienne C, et al. SKI-606, a 4-anilino-3- quinolinecarbonitrile dual inhibitor of Src and Abl kinases, is a potent antiproliferative agent against chronic myelogenous leukemia cells in culture and causes regression of K562 xenografts in nude mice. Cancer Res. 2003; 63: Kimura S, Naito H, Segawa H, et al. NS-187, a potent and selective dual Bcr-Abl/Lyn tyrosine kinase inhibitor, is a novel agent for imatinib-resistant leukemia. Blood. 2005;106: Hennequin LF, Allen J, Costello GF, et al. The discovery of AZD0530: a novel, oral, highly selective and dual-specific inhibitor of the Src and Abl family kinases [abstract]. Proc Amer Assoc Cancer Res. 2005;46: Wolff NC, Veach DR, Tong WP, Bornmann WG, Clarkson B, Ilaria RL Jr. PD166326, a novel tyrosine kinase inhibitor, has greater antileukemic activity than imatinib mesylate in a murine model of chronic myeloid leukemia. Blood. 2005;105: Dorsey JF, Jove R, Kraker AJ, Wu J. The pyrido[2,3-d]pyrimidine derivative PD inhibits p210bcr-abl tyrosine kinase and induces apoptosis of K562 leukemic cells. Cancer Res. 2000;60: Gumireddy K, Baker SJ, Cosenza SC, et al. A non-atp-competitive inhibitor of BCR-ABL overrides imatinib resistance. Proc Natl Acad Sci U S A. 2005;102: Cortes J, Albitar M, Thomas D, et al. Efficacy of the farnesyl transferase inhibitor R in chronic myeloid leukemia and other hematologic malignancies. Blood. 2003;101: Peters DG, Hoover RR, Gerlach MJ, et al. Activity of the farnesyl protein transferase inhibitor SCH66336 against BCR/ABL-induced murine leukemia and primary cells from patients with chronic myeloid leukemia. Blood. 2001;97: Hoover RR, Mahon FX, Melo JV, Daley GQ. Overcoming STI571 resistance with the farnesyl transferase inhibitor SCH Blood. 2002; 100: Reichert A, Heisterkamp N, Daley GQ, Groffen J. Treatment of Bcr/ Abl-positive acute lymphoblastic leukemia in P190 transgenic mice with the farnesyl transferase inhibitor SCH Blood. 2001;97: Marin D, Kaeda JS, Andreasson C, et al. Phase I/II trial of adding semisynthetic homoharringtonine in chronic myeloid leukemia patients who have achieved partial or complete cytogenetic response on imatinib. Cancer. 2005;103: Issa JP, Gharibyan V, Cortes J, et al. Phase II study of low-dose decitabine in patients with chronic myelogenous leukemia resistant to imatinib mesylate. J Clin Oncol. 2005;23: Kantarjian HM, O Brien S, Cortes J, et al. Results of decitabine (5-aza- 2 deoxycytidine) therapy in 130 patients with chronic myelogenous leukemia. Cancer. 2003;98: Yu C, Rahmani M, Almenara J, et al. Histone deacetylase inhibitors promote STI571-mediated apoptosis in STI571-sensitive and -resistant Bcr/ Abl+ human myeloid leukemia cells. Cancer Res. 2003;63: Nimmanapalli R, Fuino L, Stobaugh C, Richon V, Bhalla K. Cotreatment with the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) enhances imatinib-induced apoptosis of Bcr-Abl-positive human acute leukemia cells. Blood. 2003;101: Nimmanapalli R, Fuino L, Bali P, et al. Histone deacetylase inhibitor LAQ824 both lowers expression and promotes proteasomal degradation of Bcr- Abl and induces apoptosis of imatinib mesylate-sensitive or -refractory chronic myelogenous leukemia-blast crisis cells. Cancer Res. 2003;63: Guilhot F, Lacotte-Thierry L. Interferon-alpha: mechanisms of action in chronic myelogenous leukemia in chronic phase. Hematol Cell Ther. 1998;40: Barrett J. Allogeneic stem cell transplantation for chronic myeloid leukemia. Semin Hematol. 2003;40: Pinilla-Ibarz J, Cathcart K, Korontsvit T, et al. Vaccination of patients with chronic myelogenous leukemia with bcr-abl oncogene breakpoint fusion peptides generates specific immune responses. Blood. 2000;95: Cathcart K, Pinilla-Ibarz J, Korontsvit T, et al. A multivalent bcr-abl fusion peptide vaccination trial in patients with chronic myeloid leukemia. Blood. 2004;103: Bocchia M, Gentili S, Abruzzese E, et al. Effect of a p210 multipeptide vaccine associated with imatinib or interferon in patients with chronic myeloid leukaemia and persistent residual disease: a multicentre observational trial. Lancet. 2005;365: Qazilbash MH, Wieder E, Rios R, et al. Vaccination with the PR1 leukemia-associated antigen can induce complete remission in patients with myeloid leukemia [abstract]. Blood. 2004;104:77a Li Z, Qiao Y, Liu B, et al. Combination of imatinib mesylate with autologous leukocyte-derived heat shock protein and chronic myelogenous leukemia. Clin Cancer Res. 2005;11: Borrello I, Levitsky H, Damon L, et al. Vaccine-associated immune and WT-1 responses are associated with better relapse-free survival in patients with AML in remission treated with a GM-CSF secreting leukemia vaccine and autologous stem cell transplant (ASCT) [abstract]. J Clin Oncol. 2005;23 (suppl):569s. The Symposium on Oncology Practice: Hematological Malignancies will continue in the August issue. 988 Mayo Clin Proc. July 2006;81(7):