[1948] Clinicopathologic, Immunohistochemical, and Molecular Characteristics of Pleomorphic Malignant Mesothelioma

Marina Vivero, Lucian R Chirieac, Francoise Galateau-Salle. Brigham and Women's Hospital, Boston, MA; CHU Caen Cote De Nacre, Caen, France

Background: Pleomorphic malignant mesothelioma (PMM) is a variant of epithelioid malignant mesothelioma (EMM) that has recently been shown to have a worse prognosis than other variants. Short survival in PMM has prompted the suggestion that it be reclassified as a variant of sarcomatoid malignant mesothelioma (SMM), but a recent published analysis has demonstrated immunophenotypic and ultrastructural similarities to EMM. The aim of this study was to further define the histologic, immunophenotypic, and molecular characteristics of PMM.
Design: We studied 27 pleural PMMs, 24 EMMs and 11 SMMs collected between 1998 and 2011 by the French mesothelioma study panel. Tumor necrosis, mitotic index, and nuclear grade were assessed on hematoxylin and eosin-stained slides. AE1/AE3, WT-1, calretinin, CK5/6, EMA, and KL1 expression were evaluated by immunohistochemistry in all mesotheliomas, and deletion of p16 by fluorescence in-situ hybridization in PMMs and EMMs. Clinicopathologic characteristics were assessed and compared with overall survival.
Results: The PMM group included 20 males and 7 females, with a median age of 67. No major differences in demographic characteristics were present between the three groups. Necrosis was present in 74% of PMMs, 29% of EMMs, and 27% of SMMs (p=0.002). The median mitotic index per 10 high power fields was 10 in PMM, 1 in EMM and 9 in SMM (p<0.0001). High nuclear grade was present in 74% of PMMs. The overall immunophenotype of PMM reflected a pattern that more closely resembles EMM than SMM. p16 was deleted in 61% of PMMs and 74% of EMMs (p=0.5146). Overall survival in PMM was similar to SMM and worse than EMM (median OS of 7, 7, and 15 months, respectively, p=0.044).
Conclusions: Our results indicate an immunophenotypic profile in PMM more similar to EMM than SMM, despite a poor prognosis closer to that of SMM. p16 deletion rate was also similar to EMM, and different than the reported rate in SMM. This suggests that PMM should remain classified as a variant of EMM, and highlights the biologic complexity and heterogeneity of malignant mesothelioma.
Category: Pulmonary

Wednesday, March 6, 2013 1:00 PM

Poster Session VI # 279, Wednesday Afternoon


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