Materials and Methods. Results

Anatomic Pathology / Malignant Pleural Mesothelioma Histologic Assessment and Prognostic Factors of Malignant Pleural Mesothelioma Treated With Extrapleural Pneumonectomy Andrea V. Arrossi, MD, 1 E. Lin, MS, 3 David Rice, MD, 2 and Cesar A. Moran, MD 1 Key Words: Mesothelioma; Histologic types; Prognostic factors; Extrapleural pneumonectomy DOI: 10.1309/AJCPHV33LJTVDGJJ Abstract We studied 56 cases of malignant pleural mesothelioma (MPM) treated with extrapleural pneumonectomy (EPP). The slides from the EPP specimens were reviewed, and tumors were classified with the guidance of the World Health Organization classification of pleural tumors. Agreement between the histologic type from the EPP review and the diagnostic procedure (DP) reports was evaluated. Histologic and clinical parameters were also correlated with clinical outcome. There was a significant disagreement (P =.0001) between the histologic type in the DP reports and the EPP specimen review. The histologic type from the DP was associated with disease-specific survival (DSS); however, the histologic type from the EPP specimen was not associated with survival. Postoperative treatment was associated with DSS and with recurrence-free survival. Our study confirms that in many cases, final histopathologic typing of MPM is influenced by complete surgical resection and that initial biopsy should be carefully weighed in the treatment stratification. Malignant pleural mesothelioma (MPM) is the most common malignant tumor of the pleura and the one that poses more difficulty in diagnosis. Its incidence has slightly increased from /100,000 (1975) to /100,000 (2002). 1 Mesothelioma is a lethal tumor that has a relative 5-year survival rate of 6.8%. The 2-year survival is 15.3%, and females have been associated with a better prognosis (2- and 5-year relative survival rates of 19.2% and 14.3%, respectively) than males (2- and 5-year relative survival rates of 14.4% and 4.7%, respectively). 1 Age, sex, histologic type, asbestos exposure, and clinical parameters have been associated with different outcomes; however, results have been controversial. 2-19 Three main histologic types of mesothelioma epithelioid, sarcomatoid, and biphasic have been universally accepted and included in the World Health Organization (WHO) classification of pleural tumors, 20 as distinct differences in survival have been observed. 2-19 However, mesotheliomas are usually histologically heterogeneous tumors, so that different patterns in different proportions can be observed in a given tumor within a type (eg, all epithelioid) or between types (eg, mixed epithelioid and sarcomatoid). Therefore, the diagnosis and histologic typing of mesothelioma are usually influenced by the size of the tissue sample available for review. 15,21,22 Our purpose for the elaboration of this study was to critically correlate the histopathologic classification of the mesothelioma in the initial biopsy specimen and the histopathologic classification of the same tumor after an extrapleural pneumonectomy (EPP). It is known that in many cases, the initial biopsy diagnosis is considered by the treating physician as the diagnostic standard to proceed with an EPP or not. In addition, the diagnosis of biphasic tumors in biopsy material 754 Am J Clin Pathol 2008;130:754-764 754 DOI: 10.1309/AJCPHV33LJTVDGJJ

Anatomic Pathology / Original Article is not only rare but also questionable owing to the amount of tissue available for evaluation. In this series, we reviewed the histopathologic features of EPP specimens from patients treated for MPM, and we evaluated the agreement between the histologic type determined by examining biopsy or pleural fluid cytology (PFC) specimens and the histologic type of the EPP specimen as well as the prognostic significance of the histologic type from the previous diagnostic procedure (DP), biopsy or cytology, and from the EPP specimen in univariate and multivariate analyses. We also correlated patient characteristics with disease-specific survival (DSS) and recurrence-free survival (RFS). Materials and Methods From the files of the Department of Pathology, M.D. Anderson Cancer Center (MDACC), Houston, TX, we identified 75 cases of MPM that underwent EPP in an 18-year period (1986-2004). The slides and pathology reports of the surgical specimens (EPP) and the pathology reports of the diagnostic biopsy and/or PFC specimen of each case were retrieved. All biopsy material had been reviewed at the MDACC Department of Pathology before patients were considered for EPP. However, because the selection of cases dates back many years, in many cases, the initial biopsy material was returned to the original medical center from which the biopsy originated; thus, we had only our report on that biopsy. In contrast, the EPPs were performed at MDACC and the histopathologic slides were available for review except in 19 cases that were excluded from the study for this reason. The diagnosis of MPM was supported by immunoperoxidase studies and/or electron microscopy, performed in all cases, at the time of the DP and/or EPP. The H&E-stained slides from the EPP specimens were reviewed without knowledge of previous diagnosis or outcome, and we classified the tumors with the guidance of the 2004 WHO classification of pleural tumors 20 into epithelioid, sarcomatoid, biphasic, and lymphohistiocytoid types. Biphasic tumors were considered tumors that had epithelioid and sarcomatoid components, each representing at least 5% of the tumor. In addition, we documented the mitotic count, nuclear atypia (1, mild; 2, moderate; 3, severe; or 4, anaplastic nuclear features), and presence of necrosis in each case. The number of slides per case ranged from 5 to 39, with an average of 14 slides per case. Two cases had only 5 and 6 slides, respectively, owing to legal purposes. The pathology reports of the DP (tissue biopsy and/or PFC specimen) were also reviewed to determine the histologic type given to each case at the time of diagnosis. Disease extension was assessed according to the TNM staging system proposed by the International Mesothelioma Interest Group 23,24 and adapted by the American Joint Committee on Cancer, 25 taking into consideration chest and abdominal computed tomography scans, preoperative staging procedures (eg, fiberoptic bronchoscopy and exploratory laparoscopy with peritoneal washings and mediastinoscopy with lymph node sampling), intraoperative findings (at the time of EPP), and the microscopic review of the EPP specimen slides. Clinical information obtained for each patient included demographic data, administration of preoperative and/or postoperative adjuvant treatment, and follow-up, including local recurrence and/or metastasis, death, and survival time from the date of the surgery. The agreement between the histologic type of mesothelioma from the DP and the EPP specimen was calculated by using Bowker test of symmetry. The κ statistic was also calculated. Fisher exact tests were used to assess the association between variables and sex. Kaplan-Meier methods were applied to evaluate DSS and RFS. In addition, univariate and multivariate Cox proportional hazards models were used to estimate the hazard ratios of death and recurrence, including 95% confidence intervals. All computations were carried out using SAS 9.1 (SAS Institute, Cary, NC) or S-plus 7.0 (Insightful, Seattle, WA) software. Results Clinical Findings Patient characteristics are summarized in ztable 1z and ztable 2z. There were 50 men and 6 women. The median age was 60.3 years (range, 37.4-8 years). The pathologic diagnosis of mesothelioma was obtained by biopsy (thoracoscopic or needle biopsy) in 43 patients and by examination of the PFC specimen in 12 patients. For 2 patients, biopsy and PFC specimens were examined. Of the 56 patients, 26 (46%) had left-sided disease and 30 (54%) had right-sided disease. One patient had a stage I tumor (T1N0), 6 had stage II tumors (T2N0), 33 had stage III tumors (T2N1, 2; T2N2, 3; T3N0, 14; T3N1, 4; and T3N2, 10), and 14 had stage IV tumors (T4N0M0, 6; T4N1M0, 2; T4N2M0, 4; T4N3M0, 1; and T2N2M1, 1). Two patients could not have assessment of tumor staging owing to lack of essential clinical or gross pathology information. As shown in Table 2, there were no significant differences in clinical characteristics between men and women. Histologic Findings ztable 3z gives the frequencies of histologic types according to the specimen source. Review of the DP (biopsy or PFC) pathology reports yielded 37 epithelioid mesotheliomas Am J Clin Pathol 2008;130:754-764 755 755 DOI: 10.1309/AJCPHV33LJTVDGJJ 755

Arrossi et al / Malignant Pleural Mesothelioma ztable 1z Summary Statistics of Clinical Characteristics of 56 Patients With Malignant Pleural Mesothelioma * ztable 2z Summary Statistics of Clinical Characteristics by Sex of 56 Patients With Malignant Pleural Mesothelioma * Variable Result Variable Female (n = 6) Male (n = 50) P Age (y) Mean (SD) 6 (9.26) Median 60.3 Range 37.4-8 <50 4 (7) 50-60 37 (66) >60 15 (27) Female 6 (11) Male 50 (89) Side Right 30 (54) Left 26 (46) Stage I 1 (2) II 6 (11) III 33 (59) IV 14 (25) Not known 2 (4) Preoperative adjuvant treatment No 47 (84) Yes 6 (11) Not known 3 (5) Postoperative adjuvant treatment No 18 (32) Yes 33 (59) Not known 5 (9) Disease-specific death No 21 (38) Yes 30 (54) Not known 5 (9) Recurrence No 11 (20) Yes 33 (59) Not known 6 (11) Not applicable (perioperative death) 6 (11) * Data are given as number (percentage) unless otherwise indicated. Percentages may not add up to 100 due to rounding. (66%), 9 sarcomatoid mesotheliomas (16%), and 6 biphasic mesotheliomas (11%). The histologic type had not been specified in 3 tumors (5%), and for 1 tumor, there was not a previous DP report in our records. Histologic assessment of Age (y).063 <50 2 (33) 2 (4) 50-60 3 (50) 34 (68) >60 1 (17) 14 (28) Side Right 3 (50) 27 (54) Left 3 (50) 23 (46) Stage I-III 5 (83) 35/48 (73) IV 1 (17) 13/48 (27) Preoperative adjuvant treatment.13 No 4 (67) 43/47 (91) Yes 2 (33) 4/47 (9) Postoperative adjuvant treatment.64 No 1/5 (20) 17/46 (37) Yes 4/5 (80) 29/46 (63) Disease-specific death.68 No 3 (50) 18/45 (40) Yes 3 (50) 27/45 (60) Recurrence.59 No 2/5 (40) 9/39 (23) Yes 3/5 (60) 30/39 (77) * Data are given as number (percentage) or as number/total (percentage). the EPP specimens revealed 21 epithelioid (38%), 6 sarcomatoid (11%), 1 lymphohistiocytoid (2%), and 28 biphasic mesotheliomas (50%). Of the 6 biphasic tumors, 2 and 4 were predominantly (>90% of the tumor) epithelioid and sarcomatoid, respectively. The histologic types as distributed by sex are summarized in ztable 4z. The distribution of histologic type was not significantly different between men and women in DP or EPP, with P values of.77 and.16, respectively. ztable 5z shows the agreement of histologic types between DP and EPP. After review of the slides of the EPP specimens, 17 cases of epithelioid and 4 cases of sarcomatoid mesotheliomas were reclassified as biphasic tumors (46% and 44%, respectively). The Bowker test showed significant disagreement between the DP and EPP (P =.0001). ztable 3z Distribution of Histologic Types in 56 Cases of Malignant Pleural Mesothelioma * Specimen Source/Type No. (%) of Cases * Biopsy or cytology Epithelioid 37 (66) Sarcomatoid 9 (16) Biphasic 6 (11) Not applicable 1 (2) Type not specified 3 (5) Extrapleural pneumonectomy Epithelioid 21 (38) Sarcomatoid 6 (11) Biphasic 28 (50) Lymphohistiocytoid 1 (2) ztable 4z Distribution of Histologic Types by Sex in Patients With Malignant Pleural Mesothelioma * Specimen Source/Type Female Male P Biopsy or cytology.77 Epithelioid 5/5 (100) 32/47 (68) Sarcomatoid 0/5 (0) 9/47 (19) Biphasic 0/5 (0) 6/47 (13) Extrapleural pneumonectomy.16 Epithelioid 5/6 (83) 16/50 (32) Sarcomatoid 0/6 (0) 5/50 (10) Biphasic 1/6 (17) 28/50 (56) Lymphohistiocytoid 0/6 (0) 1/50 (2) * Data are given as number/total (percentage). * Percentages may not add up to 100 due to rounding. 756 Am J Clin Pathol 2008;130:754-764 756 DOI: 10.1309/AJCPHV33LJTVDGJJ

Anatomic Pathology / Original Article ztable 5z Agreement of Histologic Types by Diagnostic Procedure and Extrapleural Pneumonectomy in Malignant Pleural Mesothelioma * Extrapleural Pneumonectomy Diagnostic Procedure Epithelioid Sarcomatoid Biphasic κ Coefficient P Epithelioid 20/37 (54) 0 (0) 17 (46) Sarcomatoid 0/9 (0) 5/9 (56) 4/9 (44).54.0001 Biphasic 0/6 (0) 0/6 (0) 6/6 (100) * Data are given as number (percentage). Epithelioid Component Solid, glandular, and/or tubulopapillary patterns were observed in the pure epithelioid mesotheliomas or the epithelioid component of the biphasic mesotheliomas. The solid pattern was composed of sheets and/or nests of polygonal to cuboidal atypical cells. This pattern was observed in 40 tumors (the epithelioid component was pure solid in 4 cases, predominantly solid in 23, and focally solid in 13). The glandular pattern was formed by tubules and glands lined by cuboidal to columnar cells zimage 1Az and zimage 1Bz and was evident in 34 cases (pure glandular in 3 tumors, predominantly glandular in 10, and focally glandular in 21). Two of the glandular tumors also had focal areas with microcystic features composed of flattened or attenuated cell-lining glands, the so-called adenomatoid pattern. Tumors with tubulopapillary features were formed by papillary structures with fibrovascular cores lined by cuboidal to flattened cells and branching tubules lined by low cuboidal to columnar cells. These architectural features were present in 26 cases (pure tubulopapillary in 1 case, predominantly tubulopapillary in 7 cases, and focally tubulopapillary in 18). The 3 epithelioid patterns coexisted in 12 cases (of 40 tumors with mixed epithelioid patterns). The most frequent associations between morphologic patterns in the remaining 28 cases were solid with glandular (17 cases) and solid with tubulopapillary (10 cases). One pure epithelioid case was composed of scattered tumor cells owing to previous treatment effect. Cytologically, the cells constituting the epithelioid component of the tumors had well-demarcated borders in the majority of the cases (37 cases) with centrally located nuclei and prominent nucleoli. In 3 tumors with a solid pattern, the cells had ample eosinophilic cytoplasm with well-demarcated cell borders, displaying the so-called pavement-like arrangement. Prominent clear cells were observed in 4 tumors. The nuclear grade was 1 to 2 in 5 tumors, 2 in 17, 2 to 3 in 10, and 3 in 17. Four tumors had areas with anaplastic features (nuclear grade 4) characterized by round, polygonal, irregularly shaped, or giant cells with highly pleomorphic nuclei. The mitotic count ranged from none to 29/10 high-power fields (HPFs; 32 cases had <5 mitoses/10 HPFs, 12 had 5-9 mitoses/10 HPFs, and 5 cases had 10 or more mitoses/10 HPFs). Necrosis within the epithelioid component was present in 23 tumors, which was only focal in 4 cases. Mucinous background was present in 11 cases. Sarcomatoid Mesotheliomas Three main morphologic patterns were observed in the pure sarcomatoid mesotheliomas and the sarcomatoid component of the biphasic mesotheliomas. Only 1 pattern was seen in 20 cases ( desmoplastic type in 10, conventional sarcomatoid type in 9, and lymphohistiocytoid type in 1). Mixed conventional and desmoplastic features were present in the majority of the cases (30 tumors). In the mixed tumors, the conventional sarcomatoid type and the desmoplastic type were present only focally, at least 5%, in 2 tumors and 1 tumor, respectively. The conventional type was characterized by spindle cells arranged in sheets or fascicles zimage 1Cz. The desmoplastic type was composed of spindle cells arranged in the so-called patternless pattern in a background of dense collagenous stroma zimage 1Dz. The lymphohistiocytoid type case was formed by large, discohesive, histiocytoid-like cells admixed with an intense lymphoplasmacytic infiltrate zimage 2z. Cytologically, the cells constituting the sarcomatoid component were spindle shaped with ill-defined borders and oval to spindle nuclei. Nucleoli were conspicuous in 26 cases. The nuclear grade was 1 in 1 case, 1 to 2 in 3 cases, 2 in 17 cases, 2 to 3 in 8 cases, and 3 in 5 cases. Four cases had areas with severe nuclear anaplasia (nuclear grade 4), which was extensive in 1 tumor. The mitotic count ranged from none to 16 mitoses/10 HPFs (20 cases had <5 mitoses/10 HPFs, 6 had 5-9 mitoses/10 HPFs, and 9 had 10 or more mitoses/10 HPFs). Necrosis was seen in 15 cases. In 14 cases, 3 of which were the pure sarcomatoid type, there were areas with the so-called transitional features in which the cells are spindled and very plump, verging on an epithelioid configuration, making difficult the assessment of the histologic type (epithelioid or sarcomatoid). This pattern was predominant in 2 cases and a minor component in the remaining cases. A lymphoplasmacytic infiltrate was present in 14 tumors: focal and mild in 3, prominent in 2, diffuse and mild in 1, and moderate in the remaining cases. The cell characteristics and pattern did not qualify to classify any of these tumors as lymphohistiocytoid. Am J Clin Pathol 2008;130:754-764 757 757 DOI: 10.1309/AJCPHV33LJTVDGJJ 757

Arrossi et al / Malignant Pleural Mesothelioma A B C D zimage 1z Different patterns present in the extrapleural pneumonectomy specimen from a tumor diagnosed as epithelioid mesothelioma on biopsy. A and B, Epithelioid component (glandular-tubular pattern) (H&E, 200). C, Sarcomatoid conventional component (H&E, 200). D, Sarcomatoid desmoplastic component (H&E, 200). Treatment Of the 56 patients, 15 were treated by EPP without preoperative or postoperative treatment; 31 received postoperative intensity-modulated radiotherapy, 45 or 50 Gy, and one of the 31 had also received preoperative chemotherapy and another also received postoperative chemotherapy; 2 received only preoperative intrapleural or systemic chemotherapy; 1 received preoperative chemotherapy and radiation (at an outside institution); 1 received only postoperative chemotherapy; and 1 received preoperative and postoperative chemotherapy. Information regarding postoperative treatment was not available for 5 patients. Follow-up and Survival The overall follow-up ranged from 0 to 44.3 months. The overall DSS ranged from to 33.3 months (median, 10.7 months) zfigure 1z. Of the 56 patients, 30 (54%) died of diseaserelated causes; 4 died of unrelated causes (follow-up, 3.1-10 months); 7 were alive without disease (follow-up, 8.4-33.3 months); 3 were alive with evidence of recurrence or metastasis (follow-up, 2.5-10.5 months), and 5 died of unknown causes. One patient was alive but the recurrence status was unavailable. Six patients died from surgery-related causes. Sex, histologic type by DP, and postoperative treatment were significantly associated with DSS in the univariate Cox 758 Am J Clin Pathol 2008;130:754-764 758 DOI: 10.1309/AJCPHV33LJTVDGJJ

Anatomic Pathology / Original Article A B zimage 2z Lymphohistiocytic mesothelioma. No histologic type was provided by the pleural biopsy report of this case (A, H&E, 40; B, H&E, 200). Probability of Survival zfigure 1z Kaplan-Meier estimates to assess overall diseasespecific survival in malignant pleural mesothelioma. proportional hazards models ztable 6z. Men had around 4.5 times the risk of disease-specific death compared with women (P =.04). Patients with sarcomatoid tumors identified by the DP had around 3.0 times the risk of disease-specific death compared with patients with epithelioid tumors identified by the DP. The DSS curves by histologic types of DP and EPP are represented in zfigure 2z and zfigure 3z, respectively. The survival curve according to EPP specimens (Figure 3) shows that the log-rank test (a non parametric-based method) shows a significant P value, which is mostly due to the presence of a single case of lymphohistiocytoid mesothelioma. Indeed, the univariate Cox model (semiparametric) does not include this case in the group comparison, and, therefore, a null value is obtained. Patients with postoperative treatment had around a 70% lower risk of disease-specific death compared with patients without postoperative treatment (P =.015). Age, sex, side of the tumor, stage, histologic type by DP and EPP, preoperative treatment, and postoperative treatment were put into a multivariate Cox proportional hazards model. After model selection, only histologic type by DP and postoperative treatment were significantly associated with DSS. After adjusting for postoperative treatment, patients with DP-identified sarcomatoid tumors had approximately 3.1 times the risk of disease-specific death compared with patients with DP-identified epithelioid tumors (P =.049). After adjusting for histologic type by DP, postoperative treatment was associated with an approximately 70% lower risk of disease-specific death compared with no postoperative treatment ztable 7z. Of 56 patients, 33 (59%) had evidence of recurrence or metastasis (Table 1). The median time to recurrence was 7.82 months (mean, 8.9 months) zfigure 4z. There was recurrence in the ipsilateral pleural cavity or chest wall in 8 patients; in 4 of them metastasis had also spread to abdominal organs or lymph nodes, and 2 had involvement of the contralateral lung. Seventeen patients had recurrence in only the contralateral pleural cavity, mediastinum, or pericardium. In addition to the patients with metastasis to abdominal organs who also had local recurrence, 7 patients had compromise of the abdominal organs, 1 of whom also had involvement of the contralateral pleura. Disease outside the chest or abdominal cavity (ie, spinal soft tissues, humerus, and axillary and supraclavicular lymph nodes) occurred in 4 patients: 1 as the only metastatic site and the other 3 as part of multifocal disease with local recurrence and/or abdominal and/or contralateral chest involvement. Am J Clin Pathol 2008;130:754-764 759 759 DOI: 10.1309/AJCPHV33LJTVDGJJ 759

Arrossi et al / Malignant Pleural Mesothelioma ztable 6z Univariate Cox Proportional Hazards Models to Estimate the Association Between Covariates and Disease-Specific Survival in Malignant Pleural Mesothelioma Covariate Estimate SE P HR (95% CI) Age (y) 50-60 vs <50 1 3.51 61 (0.193-2.267) >60 vs <50 0.39 7.57 79 (0.181-2.546) Male vs female 1.50 0.74.04 4.489 (42-19.329) Side (left vs right) 0.19 0.38.62 1.211 (0.569-2.578) Stage III or IV vs I or II 0.74 1.23 2.096 (31-6.962) IV vs I-III 2 4.6 1.256 (0.535-2.951) Diagnostic procedure Sarcomatoid vs epithelioid 9 0.55.048 2.975 (10-8.760) Biphasic vs epithelioid 6 0.53.38 1.584 (0.563-4.465) Extrapleural pneumonectomy Sarcomatoid vs epithelioid 1.35 0.70.052 3.875 (0.985-15.251) Biphasic vs epithelioid 5 4.14 1.909 (10-4.496) Lymphohistiocytoid vs epithelioid 47.45 Preoperative adjuvant treatment (yes vs no) 0.35 0.75.64 0.703 (0.163-3.026) Postoperative adjuvant treatment (yes vs no) 1.16 8.015 0.313 (0.123-0.797) Recurrence (yes vs no) 16.60 CI, confidence interval; HR, hazard ratio. Probability of Survival Epithelioid Sarcomatoid Biphasic Probability of Survival Epithelioid Sarcomatoid Biphasic Lymphohistiocytoid zfigure 2z Kaplan-Meier estimates to assess disease-specific survival by histologic type according to previous diagnostic procedure in malignant pleural mesothelioma. Total number/ event for epithelioid, 32/16; for sarcomatoid, 9/5; and for biphasic, 6/5. P =.11 (log rank). zfigure 3z Kaplan-Meier estimates to assess diseasespecific survival by histologic subtype of malignant pleural mesothelioma according to extrapleural pneumonectomy specimen. Total number/event for epithelioid, 19/9; for sarcomatoid, 6/3; for biphasic, 25/17; and for lymphohistiocytoid, 1/1. P <.0001 (log rank). ztable 7z Multivariate Cox Proportional Hazards Model to Estimate the Association Between Covariates and Disease-Specific Survival in Malignant Pleural Mesothelioma Covariate Estimate SE P HR (95% CI) Biopsy or cytology Sarcomatoid vs epithelioid 1.13 0.57.049 3.082 (07-9.432) Biphasic vs epithelioid 4 0.55.66 1.273 (37-3.708) Postoperative adjuvant treatment (yes vs no) 1.22 0.51.017 96 (0.109-04) CI, confidence interval; HR, hazard ratio. 760 Am J Clin Pathol 2008;130:754-764 760 DOI: 10.1309/AJCPHV33LJTVDGJJ

Anatomic Pathology / Original Article Probability of No Recurrence zfigure 4z Kaplan-Meier estimates to assess recurrence-free survival in malignant pleural mesothelioma. In the univariate Cox proportional hazards models, only postoperative treatment was significantly associated with RFS. Patients with postoperative treatment had around a 78% decreased risk of recurrence compared with patients without postoperative treatment (P =.0012) ztable 8z. The histologic type identified by the DP or the EPP was not significantly associated with RFS. The RFS by histologic type according to DP and EPP is represented in zfigure 5z and zfigure 6z, respectively. As for the DSS by EPP specimen (Figure 3), the log-rank test of the survival curve of the RFS by EPP specimen (Figure 6) shows a significant P value, mostly owing to the single case of lymphohistiocytoid mesothelioma. Discussion As in reported demographic databases, 1 in our series of 56 cases, men were affected more than women (male/female ratio, 5:), and around 92% of the patients were older than 50 years (66% were between 50 and 60 years old). Although not statistically significant and limited by the small population, 2 (33%) of 6 women were younger than 50 years, compared with only 2 (4%) of 50 men, which may indicate a younger age of development of mesothelioma in the female population. In univariate analysis, sex was significantly associated with DSS. Men had around 4.5 times the risk of disease-specific death compared with women (P =.04). No significance of sex was found when adjusted with other significant covariates (ie, DP-identified histologic type and postoperative treatment), which could be explained by the fact that 4 of 6 women received postoperative radiotherapy. The majority of patients (59%) had stage III disease. One patient had a stage I tumor and was a woman who had been treated with preoperative chemotherapy and was alive without evidence of disease 42.1 months after the surgery. Six patients had stage II disease. Stage IV tumors were present in 25% of the patients. In all of these cases but 1, which had a retroperitoneal lymph node metastasis (M1) found at the time of surgery (the tumor was T2N2 preoperatively), tumor extension (T) was higher than estimated by preoperative procedures. Involvement of ribs in 5 cases, more than 2 chest wall foci in 4 cases, transmural pericardium in 1 case, peritoneum in 1 case, and mediastinal great vessels in 2 cases was not evident preoperatively. These findings suggest that even with the advent and implementation of invasive staging procedures such as laparoscopy with peritoneal washings ztable 8z Univariate Cox Proportional Hazards Models to Estimate the Association Between Covariates and Recurrence-Free Survival in Malignant Pleural Mesothelioma Covariate Estimate SE P HR (95% CI) Age (y) 50-60 vs <50 4 0.55.42 42 (17-1.898) >60 vs <50 0.19 0.75 26 (53-2.703) Male vs female 9 1.25 1.997 (07-6.572) Side (left vs right) 0.33 0.36.36 1.393 (83-2.843) Stage III or IV vs I or II 6 1.45 1.589 (8-5.264) IV vs I-III 5 4.31 1.569 (61-3.723) Biopsy or cytology Sarcomatoid vs epithelioid 6 8.18 1.936 (0.744-5.035) Biphasic vs epithelioid 73 0.51.87 76 (0.395-2.934) Previous cytology (sarcomatoid vs epithelioid) 17.43 5,555 0 Extrapleural pneumonectomy Sarcomatoid vs epithelioid 0.72 0.23 2.056 (36-6.649) Biphasic vs epithelioid 0 0.62 1.217 (0.560-2.647) Lymphohistiocytoid vs epithelioid 44.19 Pretreatment (yes vs no) 5 0.75.38 1.918 (39-8.371) Posttreatment (yes vs no) 1.51 7.0012 2 (88-0.548) CI, confidence interval; HR, hazard ratio. Am J Clin Pathol 2008;130:754-764 761 761 DOI: 10.1309/AJCPHV33LJTVDGJJ 761

Arrossi et al / Malignant Pleural Mesothelioma Probability of No Recurrence Epithelioid Sarcomatoid Mixed zfigure 5z Kaplan-Meier estimates to assess recurrence-free survival by histologic type of malignant pleural mesothelioma according to previous diagnostic procedure. Total number/ event for epithelioid, 26/18; for sarcomatoid, 8/6; and for mixed, 6/5. P <.39 (log rank). Probability of No Recurrence Epithelioid Sarcomatoid Mixed Lymphohistiocytoid zfigure 6z Kaplan-Meier estimates to assess recurrencefree survival by histologic type of malignant pleural mesothelioma according to extrapleural pneumonectomy specimen. Total number/event for epithelioid, 16/10; for sarcomatoid, 5/4; for mixed, 22/18; and for lymphohistiocytoid, 1/1. P <.0001 (log rank). and mediastinoscopy with lymph node sampling and refined radiographic methods, there remain a substantial number of tumors that extend beyond the clinical stage demonstrated by pathologic examination of the EPP specimen. Univariate and multivariate Cox proportional hazard models failed to reveal any significant association of tumor stage with DSS or RFS. In 2 series of 131 and 231 cases, respectively, Rusch and Venkatraman 17,19 found that there were significant differences across all stages and between T1/T2 vs T3/T4 and N0 vs N1-N3. Of the patients described in their first report, 17 50 patients had EPP, 51 patients had pleurectomy/decortication, and 30 patients had palliative pleurectomy or only exploratory thoracoscopy. The decision about surgical modality was based on the local extent of tumor. The median survival was 35 months for stage I, 16 months for stage II, 11.5 months for stage III, and 5.9 months for stage IV. In their second analysis, 19 they compiled a larger number of cases, including 115 EPP, 59 pleurectomy/ decortication, and palliative pleurectomy or only exploration in 57 patients. In this analysis, patients had a median survival of 29.9 months for stage I, 19 months for stage II, 1 months for stage III, and 8 months for stage IV. 19 This analysis of stage of disease in patients who received different treatment and surgical procedures (radical vs palliative) possibly accounts for the dissimilarity with our results. In a study of cases of MPM that underwent trimodality treatment (EPP, chemotherapy, and radiation), Sugarbaker et al 13,16,18 repeatedly found that the node status had prognostic significance. In their report of 183 patients, patients with extrapleural lymph node negative disease had 2- and 5-year survival rates of 42% and 17%, respectively, vs 23% and 0%, respectively, for patients with extrapleural node positive disease. However, they did not find survival stratification by using the TNM system for the same cohort. 18 Histologic typing of mesothelioma is thought to have an important role in prognosis; however, several studies have yielded diverse results related to differences in survival between the histologic types of MPM. In separate consecutive series of MPM from Memorial Sloan Kettering Hospital, Brenner et al 4 and Rusch and Venkatraman 17 reported significantly longer survival for patients with epithelial-type tumors vs non epithelial-type tumors. The median survival times were 15.1 and 6 months, respectively, in the analysis by Rusch and Venkatraman 17 and 16 months for epithelial tumors and 12 months for sarcomatous tumors in the study of 123 patients by Brenner et al. 4 Sugarbaker et al 13,16,18 observed repeatedly better outcomes in patients with epithelial tumors, with 2- and 5-year survival rates of 52% and 21%, respectively, vs 16% and 0% for sarcomatous or mixed histologic features. 18 Likewise, other studies also demonstrated a better outcome for patients with epithelialtype MPM. 3,6,11,12,14,15 However, treatment modalities were not uniform in any of these studies, which confers a limitation on these results. In a review of malignant mesotheliomas, including 34 cases with MPM from the Dana-Farber Cancer Institute and Brigham and Women s Hospital, Boston, MA, before the study by Sugarbaker et al, 13,16,18 Antman et al 2 had no significant differences in survival by histologic subtype, but the difference was significant when they compiled 136 cases of MPM for the analysis, with a longer survival observed for patients with epithelial type tumors. 8 762 Am J Clin Pathol 2008;130:754-764 762 DOI: 10.1309/AJCPHV33LJTVDGJJ

Anatomic Pathology / Original Article In contrast, previous series reported a lack of association between histologic type and survival. 5,7,9,10 In the series of 332 patients by Ruffie et al 9 and 83 patients by Rusch et al, 10 tumors with epithelial histologic features were associated with longer survival in univariate analyses; however, this difference was not statistically significant in multivariate analyses. Different treatment modalities had been used as well. In our study, the histologic type reported in the previous DP (biopsy or cytology) was significantly associated with DSS in univariate and multivariate analyses but not with the RFS. Patients whose previous biopsy or cytology diagnoses were sarcomatoid tumors had approximately 3.1 times the risk of disease-specific death compared with patients whose previous biopsy or cytology diagnoses were epithelioid tumors (P =.049). By using the EPP specimen as reference, the sarcomatoid tumors had an increased risk of disease-specific death, although this difference was not significant (P =.052), nor was it significant for the RFS. It has been reported that the size of the tissue specimens obtained for histopathologic diagnosis influences the type diagnosis of MPM. 16,21,22,26 Bueno et al 26 investigated the accuracy of tumor diagnosis and histologic subclassification before initiation of trimodality therapy in 305 cases with a final diagnosis of MPM at EPP. Their specificity for a diagnosis of epithelial-type mesothelioma with pleural biopsy was 56%. Around 20% and 36% of tumors diagnosed as epithelial- and sarcomatoid-type mesotheliomas, respectively, in the previous pleural biopsy specimen were reclassified with a different histologic type in the EPP pathology report (desmoplastic tumors were excluded from this analysis). There is, however, no mention of criteria used to classify tumors as mixed (ie, percentage of different components). In our study, 46% of cases of epithelioid mesotheliomas and 44% of cases of sarcomatoid mesotheliomas were reclassified as biphasic tumors after review of the EPP specimens. These results confirm a higher percentage of biphasic tumors encountered in EPP specimens. The greater number of biphasic tumors is most likely due to the fact that, even though we used the WHO classification as a guide for the histologic assessment of the tumors, we classified biphasic tumors as tumors showing at least 5% of each component. According to the WHO classification, biphasic tumors should contain at least 10% of each component (epithelioid and sarcomatoid) to be classified as such and desmoplastic mesotheliomas should contain at least 50% of desmoplastic features. 20 The amount of each component in biphasic tumors was not specified in the previous studies. 2-13,15-19,27 Further investigation is needed to define the biphasic tumors in terms of survival because there might be different groups of biphasic tumors that behave as epithelioid or sarcomatoid tumors according to the amount of epithelioid or sarcomatoid/ desmoplastic component present. The optimal management of MPM has not been established. More than one modality is favored. Surgery is recommended, especially for localized or locally advanced tumors that are potentially resectable. Radical surgical alternatives include pleurectomy/decortication and EPP. Because pleurectomy conveys limited cytoreduction and inability to administer tumoricidal doses of radiation following surgery owing to the risk of injury to the remaining lung, EPP has become widely accepted. In a phase 2 study of high-dose postoperative radiotherapy, Rusch et al 27 showed decreased local recurrence rates for patients undergoing EPP followed by high-dose radiation. In their study, the median survival time was 33.8 months for patients with stage I or II (International Mesothelioma Interest Group) disease and 10 months for patients with stage III or IV disease, suggesting that combined treatment seems to confer a survival benefit for early-stage tumors. Our study supports this hypothesis because patients who received postoperative treatment had approximately 70% and 78% decreased risks of disease-specific death and recurrence, respectively, compared with patients who did not receive postoperative treatment. Conclusions The prognostic significance of the histologic type provided by the DP is uncertain because a great number of cases will be histologically reclassified when the EPP is available. Treatment stratification should not be based on the histologic type of MPM determined on limited tissue samples until further investigation has been done and better definition of biphasic tumors accomplished. Multimodality treatment including radiotherapy as postoperative treatment is associated with longer survival. From the Departments of 1 Anatomic Pathology, 2 Thoracic Surgery, and 3 Biostatistics and Applied Mathematics, the University of Texas M.D. Anderson Cancer Center, Houston. Address reprint requests to Dr Arrossi: Dept of Pathology, L25, the Cleveland Clinic Foundation, 9500 Euclid Ave, Cleveland, OH 44195. References 1. National Cancer Institute. SEER Cancer Statistics Review 1975-2003. http://seer.cancer.gov/csr/1975_2003/results_ merged/sect_17_mesothelioma.pdf. Accessed January 2007. 2. Antman KH, Blum RH, Greenberger JS, et al. Multimodality therapy for malignant mesothelioma based on a study of natural history. Am J Med. 1980;68:356-362. 3. Chahinian AP, Pajak TF, Holland JF, et al. Diffuse malignant mesothelioma: prospective evaluation of 69 patients. Ann Intern Med. 1982;96(6 pt 1):746-755. Am J Clin Pathol 2008;130:754-764 763 763 DOI: 10.1309/AJCPHV33LJTVDGJJ 763

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