LISA A. CAREY. The University of North Carolina, Chapel Hill, North Carolina, USA

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1 The Oncologist Directed Therapy of Subtypes of Triple-Negative Breast Cancer LISA A. CAREY The University of North Carolina, Chapel Hill, North Carolina, USA Key Words. Triple-negative breast cancer Chemotherapy Epidermal growth factor receptor Vascular endothelial growth factor receptor Antiangiogenesis BRCA1 Poly(ADP-ribose) polymerase Cetuximab Bevacizumab Olaparib BSI-201 Disclosures: Lisa A. Carey: Consultant/advisory role: sanofi-aventis, BiPar, Wyeth, Pfizer, Genentech, Bristol-Myers Squibb, Novartis (all uncompensated); Research funding/contracted research: GlaxoSmithKline, Boehringer-Ingelheim, Genentech, Wyeth, Bristol-Myers Squibb (all uncompensated). The content of this article has been reviewed by independent peer reviewers to ensure that it is balanced, objective, and free from commercial bias. No financial relationships relevant to the content of this article have been disclosed by the independent peer reviewers. ABSTRACT In developed countries, there has been a remarkable improvement in mortality from breast cancer, but almost all of that benefit has occurred in the estrogen receptor (ER) and human epidermal growth factor receptor (HER)-2 subsets. Triple-negative breast cancer, defined as tumors that are negative for ER, progesterone receptor, and HER-2, represent a minority of breast cancers. However, because of the poor prognosis in this particular subtype, triple-negative disease accounts for a disproportionate number of metastatic cases and breast cancer deaths. While chemotherapy is effective in triple-negative disease, research continues to better target therapies and predict prognosis. Recent studies have suggested a link between BRCA mutations and triple-negative disease, but the nature of this link remains opaque. Antiangiogenic agents such as bevacizumab have demonstrated efficacy across subtypes. More recently, poly(adp-ribose) polymerase inhibitors appear to take advantage of the concept of synthetic lethality, or dual pathway inhibition, in attacking triple-negative and BRCA-associated tumors. These and other studies in triple-negative disease will help us to better identify effective treatment options and improve outcomes in these patients. This article addresses the nature of, and therapeutic strategies for, triple-negative breast cancer. The Oncologist 2011;16(suppl 1):71 78 INTRODUCTION Triple-negative breast cancer, defined as tumors that are negative for estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor (HER)-2, represent a minority of breast cancers. However, because of the poor prognosis in this particular subtype, triple-negative disease accounts for a disproportionate number of metastatic cases and breast cancer deaths. Like any other subtype of breast cancer, triple-negative disease generally presents as early breast cancer. A classic case is shown in Figure 1 of a stage II breast cancer patient with a baseline risk for recurrence of approximately 60%, based on tumor size and nodal status. In a hormone recep- Correspondence: Lisa A. Carey, M.D., University of North Carolina, 170 Manning Drive, 3rd Floor, Chapel Hill, North Carolina , USA. Telephone: ; Fax: ; lisa_carey@med.unc.edu Reprinted from The Oncologist 2010;15(suppl 5): AlphaMed Press /2010/$30.00/0 doi: /theoncologist.2011-S1-71 The Oncologist 2011;16(suppl 1):

2 72 Figure 1. Adjuvant therapy for early breast cancer (90% are early at diagnosis). Abbreviations: ER, estrogen receptor; HER-2, human epidermal growth factor receptor; PR, progesterone receptor. tor positive breast cancer patient at high risk, endocrine therapy is added to chemotherapy, and the residual risk for relapse is well under 25%. For those that are HER-2, anti HER-2 therapy is added, and again, there is a substantial improvement in outcome because of the addition of a targeted therapy to chemotherapy. Meanwhile, in triple-negative disease, clinicians are entirely reliant on chemotherapy. Chemotherapy has certainly improved over the years, but with chemotherapy alone the residual risk remains substantially higher, between 30% and 40%. Improving outcomes in triple-negative disease will require better understanding of the biology and drug targets in this subtype. MOLECULAR SUBTYPES IN TRIPLENEGATIVE DISEASE Triple-negative disease encompasses more than one molecular subtype. The major components of triple-negative tumors in molecular assays are the basal-like and, more recently, the uncommon but intriguing claudin-low molecular subtypes. Basal-like breast cancers have several molecular characteristics. These include low signals for the ER-related gene cluster and the HER-2 related gene clusters (Fig. 2). For this reason, these tumors generally (although not always) are negative for ER, PR, and HER-2 on clinical assays. Basal-like tumors express proliferation genes and a unique cluster of genes, called the basal cluster, which includes basal cytokeratins and epidermal growth factor receptor (EGFR). They are often p53 mutant and have evidence of genomic instability, which may be therapeutically relevant (Fig. 3) [1, 2]. It is becoming clear that the triple-negative phenotype on clinical assays enriches for basal-like cancer, but there is discordance between these two groups. Approximately 25% of triple-negative breast cancers are not basal-like on gene expression array (Fig. 4). Similarly, there are basal-like breast cancers that are not tri- Directed Therapy in Triple-Negative Breast Cancer Figure 2. Intrinsic breast cancer subtypes. Abbreviations: ER, estrogen receptor; HER-2, human epidermal growth factor receptor; PR, progesterone receptor. Figure 3. The picture of basal-like breast cancer. Abbreviations: EGFR, epidermal growth factor receptor; ER, estrogen receptor; HER-2, human epidermal growth factor receptor. ple-negative, which also represent approximately 25% of cases. Therefore, in clinical trials looking at basal-like biology and using the triple-negative phenotype to identify patients, the potential exists for misclassification. Limited information currently exists about the claudinlow subtype, and this is an exciting area of research. Claudin-low subtype tumors represent only approximately 5% of tumors and fall under the triple-negative spectrum. Among the intriguing features of the claudin-low subtype is its expression of stem cell features; some recent data suggest that these features are enriched in post-treatment tumors (Fig. 5) [3, 4]. Intrinsic subtypes, although not initially developed for prognostication, are actually useful in this application. Several studies have demonstrated that the best prognosis is seen with the luminal A subtype. Patients with the basallike, the HER-2 (before HER-2 targeting), and the claudinlow subtypes, which make up the triple-negative tumors, have a significantly poorer outcome.

3 Carey 73 Figure 4. Triple-negative phenotype and molecular sybtypes. Abbreviations: HER-2, human epidermal growth factor receptor; IHC, immunohistochemistry. Figure 5. Claudin-low subtype (recently described, still lots of questions). From Herschkowitz JI, Simin K, Weigman VJ et al. Identification of conserved gene expression features between murine mammary carcinoma models and human breast tumors. Genome Biology 2007;8:R76. Originally published by BioMed Central; and Creighton CJ, Li X, Landis M. Residual breast cancers after conventional therapy display mesenchymal as well as tumor-initiating features. PNAS 2009;106: , with permission. CLINICAL CHARACTERISTICS OF TRIPLE-NEGATIVE DISEASE SUBTYPES A study from the population-based Carolina Breast Cancer Study provided the first illustration of the clinical characteristics of breast cancer subtypes. Among the most interesting findings was that younger women and African- American women were far more likely to develop the basallike subtype compared with other groups. Although these subtypes are associated with prognosis, this is not because of a higher disease stage at presentation or higher degree of nodal involvement. The basal-like subtype was almost entirely invasive ductal carcinomas, and almost all were grade III with a high rate of p53 mutations (Table 1) [5]. Patients with triple-negative disease tend to have a higher risk for early relapse, with an early peak then drop (Fig. 6) [6]. As has been noted in several data sets, the risk for relapse of a triple-negative breast cancer after about 5 years is less than that of a hormone receptor positive breast cancer. Until recently, this long-term impact and switching over of relapse risk was something that was relatively underrecognized in triple-negative disease. In addition to the higher risk for early relapse, the sites of involvement of the different subtypes seem to be different. Another analysis found that patients with triple-negative breast cancer had a high risk for visceral involvement upon relapse, and a relatively low risk for bone involvement compared with, for example, patients with the more common ER subtypes (Table 2) [7]. Other data sets have shown an elevated risk for central nervous system involvement at some point during the disease in triple-negative tumors, up to 46% in one study [8]. TREATMENT OPTIONS IN TRIPLE- NEGATIVE DISEASE Chemotherapy is known to be effective in triple-negative disease, and advances in chemotherapy have particularly benefited this patient group. Data also exist to suggest that antiangiogenic drugs work in triple-negative breast cancer, to the same extent that they probably work in all breast cancer subtypes. An effective selection strategy is not currently available for determining which patients could benefit the most from these agents. Potential approaches in triple-negative disease include more targeted chemotherapy, growth factor pathway approaches, and BRCA1-driven approaches. Although there is a common misconception that triple-negative tumors are less sensitive to chemotherapy, conventional agents are effective in these patients. Two independent data sets evaluating anthracycline/ taxane-based regimens in the neoadjuvant setting reported high rates of pathologic complete response (pcr) in patients with triple-negative disease (Table 3) [9, 10]. Conventional regimens therefore remain the standard of care for patients with this subtype, particularly in the adjuvant setting. In addition, the prognostic implications of a pcr are still true in this subtype as they are in all subtypes. One data set looking at pcr versus residual disease and outcome found that triple-negative patients achieving a pcr to neoadjuvant chemotherapy had an excellent outcome, but those who failed to achieve a pcr had a higher risk for relapse than patients with the non triple-negative subtype. This was a result, in part, of the fact that patients with other subtypes, particularly the luminal breast cancers, received and responded to adjuvant endocrine therapy (Fig. 7). ANTIANGIOGENIC APPROACHES IN TRIPLE- NEGATIVE DISEASE Many antiangiogenic treatments have been introduced or are currently under development, and may hold promise for

4 74 Directed Therapy in Triple-Negative Breast Cancer Table 1. Subtype characteristics at diagnosis Basal-like (n 100) HER-2 /ER (n 33) Luminal A (n 255) Luminal B (n 77) p-value AA premenopausal 39% 9% 36% 9% Postmenopausal 14% 7% 59% 16%.001 White premenopausal 16% 6% 51% 18% Postmenopausal 16% 6% 58% 16% Stage I 24% 28% 44% 39%.06 II 62% 53% 47% 54% III IV 13% 19% 9% 6% Lymph node positive 41% 56% 34% 47%.04 Invasive ductal 84% 94% 70% 79% Invasive lobular % 7% Mixed 6% 6% 9% 12%.001 Poor histologies 10% 0 3% 1% Grade III 84% 75% 31% 31%.001 p53 mutated 44% 43% 15% 23%.001 Abbreviations: AA, African-American; ER, estrogen receptor; HER-2, human epidermal growth factor receptor 2. From Carey LA, Perou CM, Livasy CA et al. Race, breast cancer subtypes, and survival in the Carolina Breast Cancer Study. JAMA 2006;295: Copyright 2006 American Medical Association. All rights reserved. Figure 6. Triple-negative breast cancer behavior. Adapted and reprinted by permission from the American Association for Cancer Research: Dent R, Trudeau M, Pritchard KI et al. Triple-negative breast cancer: Clinical features and patterns of recurrence. Clin Cancer Res 2007;13: Table 2. Heterogeneity in relapse site by subtype Sites involved N Bone Soft Tissue Viscera TNBC 79 13% 13% 74% ER % 7% 54% HER % 12% 81% Abbreviations: ER, estrogen receptor; HER-2, human epidermal growth factor receptor 2; TNBC, triplenegative breast cancer. Based on Liedtke C, Mazouni C, Hess KR et al. Response to neoadjuvant therapy and long-term survival in patients with triple-negative breast cancer. J Clin Oncol 2008;26: Reprinted with permission American Society of Clinical Oncology. All rights reserved. patients with triple-negative breast cancer. Bevacizumab has the most data in breast cancer. Trials with bevacizumab include the Eastern Cooperative Oncology Group 2100 trial, a randomized phase III trial of bevacizumab added to weekly paclitaxel in first-line therapy for breast cancer. This was a relatively unselected group of patients, except that there were few HER-2 patients included in the study population. As shown in Figure 8, the addition of bevacizumab to weekly paclitaxel led to a substantially higher probability of progression-free survival (PFS) [11]. Particularly with an expensive drug such as bevacizumab, researchers were interested in further identifying specific subsets of patients who benefited from the therapy in a larger, relatively unselected population of patients. Although specific clinical subsets that benefited were not well characterized in further analyses, it was determined that patients with triple-negative disease benefited as much as, if not more than, the average [11]. This was also demonstrated in some subset analyses of tyrosine kinase inhibitor approaches, including vascular endothelial growth factor receptor inhibition. BASAL-LIKE BREAST CANCER AND BRCA1 Researchers have long recognized that, when women who carry germ-line mutations in BRCA1 develop breast cancer,

5 Carey 75 Table 3. Chemosensitivity: Pathologic complete response (complete tumor eradication) to preoperative chemotherapy [9, 10] T-FAC (N 82)* AC-T (n 107)* Luminal A/B 7% 7% Normal-like 0 NA HER-2 /ER 45% 36% Basal-like/triple-negative 45% 26% Basal-like/triple-negative breast cancer responds to anthracycline/taxane-based chemotherapy. Conventional chemotherapy regimens remain standard of care. Adapted and reprinted by permission from the American Association for Cancer Research: Rouzier R, Perou CM, Symmans WF et al. Breast cancer molecular subtypes respond differently to preoperative chemotherapy. Clin Cancer Res 2005;11: ; and Carey LA, Dees EC, Sawyer L et al. The triple negative paradox: primary tumor chemosensitivity of breast cancer subtypes. Clin Cancer Res 2007;13: Figure 8. ECOG 2100: Randomized phase III trial of bevacizumab added to paclitaxel in stage IV breast cancer. Abbreviations: ECOG, Eastern Cooperative Oncology Group; HER-2, human epidermal growth factor receptor; HR, hazard ratio; PFS, progression-free survival. From Miller K, Wang M, Gralow J et al. Paclitaxel plus bevacizumab versus paclitaxel alone for metastatic breast cancer. N Engl J Med 2007;357: Copyright 2007 Massachusetts Medical Society. All rights reserved. Figure 7. Responsiveness to conventional chemotherapy. Abbreviations: pcr, pathologic complete response; RD, residual disease; TNBC, triple-negative breast cancer. From Liedtke C, Mazouni C, Hess KR et al. Response to neoadjuvant therapy and long-term survival in patients with triple-negative breast cancer. J Clin Oncol 2008;26: Reprinted with permission American Society of Clinical Oncology. All rights reserved. Figure 9. Basal-like breast cancer and BRCA1. From Sorlie T, Tibshirani R, Parker J et al. Repeated observation of breast tumor subtypes in independent gene expression data sets. Proc Natl Acad Sci U S A 2003;100: , with permission. most of the time those breast cancers are in fact the basallike molecular subtype. However, whereas most BRCA1 carriers have basal-like breast cancer, most basal-like breast cancers arise in women who do not have inherited BRCA1 mutations. Although biologic data and preclinical data suggest that there is some aberration in the BRCA1 pathway, the exact mechanisms have not been found. Nevertheless, there are shared characteristics between tumors arising in BRCA1 mutation carriers and sporadic tumors (Figure 9) (Table 4) [12, 13]. These include a variety of pathologic features, as well as a high p53 mutation rate, the basal phenotype, EGFR expression, and an X-chromosome inactivation pattern. One therapeutically relevant characteristic is sensitivity to DNA damage, and sensitivity to DNA-damaging agents is a hallmark across these groups [13]. Researchers are interested in the similarities between BRCA1 and sporadic basal-like breast cancers because BRCA1 plays an important role in mediating the DNA damage response. This has implications for targeted agents, including poly- (ADP-ribose) polymerase (PARP) inhibitors, and also for certain chemotherapeutic agents. Certain DNA-damaging agents, particularly ionizing radiation and double-strand DNA damaging agents like platinum agents, may be particularly effective in BRCA1-

6 76 Directed Therapy in Triple-Negative Breast Cancer Table 4. BRCAness : Characteristics shared between BRCA-associated and sporadic breast cancers High grade ER and HER-2 C-myc amplified Medullary Pushing margins DCIS less common Lymphocytic infiltrate TP53 mutations Basal phenotype EGFR expression X-chromosome inactivation pattern Sensitivity to DNA damage Abbreviations: DCIS, ductal carcinoma in situ; EGFR, epidermal growth factor receptor; ER, estrogen receptor; HER-2, human epidermal growth factor receptor 2. Adapted from Turner N, Tutt A, Ashworth A. Hallmarks of BRCAness in sporadic cancers. Nat Rev Cancer 2004;4: Table 5. Olaparib in BRCA1 /BRCA2 breast cancer: results Response measure in intent-to-treat cohort Olaparib 400 mg twice daily (n 27) Olaparib 100 mg twice daily (n 27) Overall response, n (%) 11 (41) 6 (22) Complete response, n (%) 1 (4) 0 Partial response, n (%) 10 (37) 6 (22) Toxicity included: fatigue (56%), nausea/vomiting ( 40%), headache (37%); mostly mild/moderate. 30% of patients were given reduced doses and 30% had delayed doses because of toxicity. From Tutt A, Robson M, Garber JE et al. Phase II trial of the oral PARP inhibitor olaparib in BRCA-deficient advanced breast cancer abstract CRA501. J Clin Oncol 2009;27(18 suppl). Reprinted with permission American Society of Clinical Oncology. All rights reserved. Figure 10. BRCA1 dysfunction and PARP inhibition. Abbreviations: BER, base excision repair; HR, hormone receptor; PARP, poly(adp-ribose) polymerase. Adapted from Comen EA, Robson M. Inhibition of poly(adp)-ribose polymerase as a therapeutic strategy for breast cancer. Oncology (Williston Park) 2010;24: deficient tumors. In the setting of DNA damage, BRCA1 in part functions in cell cycle arrest allowing repair, which would confer resistance to these agents because the cell would be able to repair the damage that the drug had caused. If BRCA1 function is lost, the DNA damage checkpoint is lost, the cell does not have an opportunity to repair itself, and it is killed by such chemotherapy. Therefore, DNAdamaging agents may be particularly toxic to these cells [14]. It is important to note that these concepts are only theoretical at this point, because few supporting clinical studies are available; moreover, it is not yet clear that the same effect would hold true in both BRCA1-associated and sporadic tumors with BRCAness [15]. Figure 11. EGFR in basal-like breast cancer. Abbreviations: CK, cytokeratin; EGFR, epidermal growth factor receptor; HER-2, human epidermal growth factor receptor; IHC, immunohistochemistry: TMA, tissue microarray. BRCA AND TRIPLE-NEGATIVE DISEASE: CHALLENGES IN THE CLINICAL SETTING Although there may be a connection between BRCA and triple-negative disease, there have been challenges in moving from preclinical research to clinical practice. One retrospective analysis evaluated neoadjuvant therapy in 102 patients with BRCA1 germ-line mutations treated with a variety of neoadjuvant chemotherapy combinations, including a prospective trial of a few patients treated with cisplatin alone. A pcr rate of 83% was observed in the cisplatin-only group, compared with 22% for all the other regimens. Although this retrospective study had certain baseline confounding issues, it suggests particular sensitivity to cisplatin among BRCA1 mutation carriers [16]. Meanwhile, another prospective trial was conducted in

7 Carey triple-negative patients, all of whom received cisplatin monotherapy, and the pcr rate was only 22% [17]. Therefore, it still remains to be seen whether BRCA status can be used as a surrogate for response in triple-negative patients. PARP INHIBITION IN TRIPLE-NEGATIVE DISEASE As mentioned previously, PARP inhibition may be another therapeutically valuable mechanism in patients with triplenegative disease. PARP inhibition involves synthetic lethality, meaning cell death by targeting more than one pathway, when impairment of one pathway alone is not lethal (Fig. 10) [18]. In a normal cell receiving certain types of DNA damage, several opportunities exist to repair that damage, including homologous recombination, which is BRCA1-dependent, or base excision repair (BER), highlighted because it is a PARP-dependent function. Essentially, synthetic lethality means that if one mechanism is lost, the cell remains viable; however, if both routes are lost, the cell loses both primary and alternate methods for DNA repair, and dies. Some clinical data are available to support this approach. One phase II study of olaparib, an oral PARP inhibitor, was conducted in pretreated BRCA1 or BRCA2 mutation carriers. Olaparib was administered at two doses, 100 mg or 400 mg, twice daily. The primary endpoint was clinical response. Most enrollees were BRCA1 mutations carriers, and half were triple-negative. All enrollees had received prior chemotherapy. The results were remarkable; in a pretreated group with a single-agent PARP inhibitor, 41% exhibited response to therapy with the 400-mg dose, and some responded in the much lower 100-mg dose (Table 5). It should be noted that some toxicity with olaparib was reported. Fatigue was quite prominent, as were gastrointestinal effects, and about 30% of the patients had to either reduce the dose or delay doses because of toxicity [19]. While initial data with PARP inhibitors are promising, it is important to stress the need for proper patient selection. For instance, these agents may prove to be effective only in patients with BRCA1 or BRCA2 mutations. Likewise, it may be necessary to deliver these drugs with a DNA-damaging agent to induce synthetic lethality. None of the PARP inhibitors has been commercially approved, and additional findings from large-scale trials are needed to better characterize their potential role in clinical practice. Another PARP inhibitor, BSI-201, is an i.v. agent studied in a randomized phase II trial of patients with metastatic triple-negative disease. Patients who had minimal previous treatment were randomized to receive gemcitabine plus carboplatin either alone or with the addition of BSI-201. The response rate was surprisingly low in the chemotherapyonly arm at only 16%, but it was substantially higher, 48%, Table 6. Gemcitabine and carboplatin with or without BSI-201: results Gem/Carbo (n 44) BSI-201 Gem/Carbo (n 42) p-value Objective response, 7 (16%) 20 (48%).002 n (%) Clinical benefit rate 9 (21%) 26 (62%).0002 Safety: no differences in hematologic or nonhematologic toxicities; no differences in gemcitabine/carboplatin dose reductions between study arms. From O Shaughnessy J, Osborne C, Pippen J et al. Final results of a randomized phase II study demonstrating efficacy and safety of BSI-201, a poly(adp-ribose) polymerase (PARP) inhibitor, in combination with gemcitabine/carboplatin (G/C) in metastatic triple negative breast cancer (TNBC) [abstract 3122]. Presented at the 2009 San Antonio Breast Cancer Symposium, San Antonio, Texas, December in the arm that received chemotherapy in addition to the PARP inhibitor (Table 6). There were essentially no differences in either hematologic or nonhematologic toxicities between the two treatment groups, suggesting that BSI-201 was very well tolerated and had a profound impact in triplenegative disease. The PFS intervals were increased from about 3 months to nearly 7 months. Even more impressively, in a phase II study there was a survival advantage with the addition of BSI-201 from a median of just under 8 months to over 12 months [20]; results from the definitive phase III trial are pending. EGFR IN BASAL-LIKE BREAST CANCER:LESSONS LEARNED TRIPLE-NEGATIVE DISEASE EGFR is part of the basal cluster, and has been of interest in preclinical studies for a number of years. Researchers have shown that EGFR is present and expressed on tissue microarrays from basal-like tumors, and that the cell lines representing basal-like breast cancer are EGFR dependent for growth and proliferation. Consequently, EGFR has been considered as a sensible target in basal-like breast cancer (Fig. 11). Several clinical studies have evaluated this approach. In the Translational Breast Cancer Research Consortium (TBCRC) 001 study, cetuximab, which is an anti-egfr monoclonal antibody, was added to carboplatin therapy in a pretreated triple-negative cohort, with a modest response rate of 17% (Table 6) [21]. Meanwhile, in a subset of the U.S. Oncology trial, the addition of cetuximab to carboplatin and irinotecan led to a higher response rate, 49% versus 30%, but did not improve the PFS interval (Table 6) [22]. What did we learn from these studies? Among the most interesting data came from a subset of patients in

8 78 Directed Therapy in Triple-Negative Breast Cancer TBCRC 001 who permitted serial biopsies of their tumor before and after cetuximab. Although the vast majority of patients had tumors with EGFR expression and pathway activation by gene expression array, in only 25% of these tumors was the EGFR pathway deactivated; all clinical benefit was seen in this small group. In the other 75%, the drug was ineffective [22], likely due to alternate mechanisms of activation that have yet to be discovered. We are likely to face similar challenges with other targeted therapies; incorporating tissue-based studies into clinical trials safely and effectively is the only way for us to truly understand the biology of breast cancer and the impact of our drugs. CONCLUSIONS In developed countries, there has been a remarkable improvement in mortality from breast cancer, but almost all of that benefit has occurred in the ER and HER-2 subsets. Triple-negative disease remains the biggest challenge moving forward, but we are close to improved, treatment options and outcomes for these patients. REFERENCES 1 Perou CM, Sorlie T, Eisen MB et al. Molecular portraits of human breast tumours. Nature 2000;406: Sorlie T, Perou CM, Tibshiranie R, et al. Gene expression patterns of breast carcinomas distinguish tumor subclasses with clinical implications. PNAS 2001;98: Herschkowitz JI, Simin K, Weigman VJ et al. Identification of conserved gene expression features between murine mammary carcinoma models and human breast tumors. Genome Biology 2007;8:R76. 4 Creighton CJ, Li X, Landis M. Residual breast cancers after conventional therapy display mesenchymal as well as tumor-initiating features. PNAS 2009;106: Carey L, Perou CM, Livasy CA et al. Race, breast cancer subtypes, and survival in the Carolina Breast Cancer Study. JAMA 2006;295: Study. JAMA 2006;295: Dent R, Trudeau M, Pritchard KI et al. Triple-negative breast cancer: Clinical features and patterns of recurrence. Clin Cancer Res 2007;13: Liedtke C, Mazouni C, Hess KR et al. Response to neoadjuvant therapy and long-term survival in patients with triple-negative breast cancer. J Clin Oncol 2008;26: Lin NU, Claus E, Sohl J et al. Sites of distant recurrence and clinical outcomes in patients with metastatic triple-negative breast cancer: High incidence of central nervous system metastases. Cancer 2008;113: Rouzier R, Perou CM, Symmans WF et al. Breast cancer molecular subtypes respond differently to preoperative chemotherapy. Clin Cancer Res 2005;11: Carey LA, Dees EC, Sawyer L et al. The triple negative paradox: primary tumor chemosensitivity of breast cancer subtypes. Clin Cancer Res 2007; 13: Miller K, Wang M, Gralow J et al. Paclitaxel plus bevacizumab versus paclitaxel alone for metastatic breast cancer. N Engl J Med 2007;357: Sorlie T, Tibshirani R, Parker J et al. Repeated observation of breast tumor subtypes in independent gene expression data sets. Proc Natl Acad Sci U S A 2003;100: Turner N, Tutt A, Ashworth A. Hallmarks of BRCAness in sporadic cancers. Nat Rev Cancer 2004;4: Hoeijmakers JHJ. Genome maintenance mechanisms for preventing cancer. Nature 2001;411: Kennedy RD, Quinn JE, Mullan PB et al. The role of BRCA1 in the cellular response to chemotherapy. J Natl Cancer Inst 2004;96: Byrski T, Gronwald J, Huzarski T et al. Pathologic complete response rates in young women with BRCA1-positive breast cancers after neoadjuvant chemotherapy. J Clin Oncol 2010;28: Silver, D, Richardson, AL, Eklund, AC et al. Efficacy of Neoadjuvant Cisplatin in Triple-Negative Breast Cancer. J Clin Oncol 2010; 28: Comen EA, Robson M. Inhibition of poly(adp)-ribose polymerase as a therapeutic strategy for breast cancer. Oncology (Williston Park) 2010;24: Tutt A, Robson M, Garber JE et al. Phase II trial of the oral PARP inhibitor olaparib in BRCA-deficient advanced breast cancer. J Clin Oncol 2009; 27(18 suppl):abstract CRA O Shaughnessy J, Osborne C, Pippen J et al. Final results of a randomized phase II study demonstrating efficacy and safety of BSI-201, a poly(adpribose) polymerase (PARP) inhibitor, in combination with gemcitabine/ carboplatin (G/C) in metastatic triple negative breast cancer (TNBC) [abstract 3122]. Presented at the 2009 San Antonio Breast Cancer Symposium, San Antonio, Texas, December Carey LA, Rugo HS, Marcom PK et al. TBCRC 001: EGFR inhibition with cetuximab added to carboplatin in metastatic triple-negative (basal-like) breast cancer. J Clin Oncol 2008;26(15 suppl):abstract O Shaughnessy J, Weckstein DJ, Vukeelja SJ et al. Preliminary results of a randomized phase II study of weekly irinotecan/carboplatin with or without cetuximab in patients with metastatic breast cancer [abstract 308]. Presented at the 2007 San Antonio Breast Cancer Symposium, San Antonio, Texas, December 2007.