Pleomorphic Epithelioid Diffuse Malignant Pleural Mesothelioma: A Clinicopathological Review and Conceptual Proposal to Reclassify as Biphasic or Sarcomatoid Mesothelioma

Abstract

Our finding that the pleomorphic subtype is a predictor of aggressive behavior in epithelioid DMPM with no survival difference from biphasic or sarcomatoid DMPM suggests that it may be best regarded as a sarcomatoid pattern rather than a subtype of epithelioid DMPM.

Pleomorphic mesothelioma: report of 10 cases

“…That all of the pleomorphic mesotheliomas in the present series were characterized by marked cellular discohesion, high mitotic activity and prominent epithelioid morphology, including the presence in some cases of poorly formed tubular or papillary structures (Figures 1a and 3h) or deciduoid features (Figure 3a), supports the current belief that these tumors should be regarded as a high-grade variant of epithelioid mesothelioma, 19 and should not be reclassified as sarcomatoid mesotheliomas as has recently been proposed by some authors. 9 Further support for this position is also provided by the electron microscopic finding, in the present investigation, of a large number of long slender microvilli that were frequently seen on the cell membrane of the neoplastic cells. This is in contrast to sarcomatoid mesotheliomas in which the cell membranes are usually devoid of microvilli, and if such structures are present, they are sparse and rudimentary.…”

“…Based on their light microscopic features, the 2004 WHO Classification defines four major histologic subtypes of diffuse malignant mesothelioma: epithelioid, sarcomatoid, mixed epithelioid and sarcomatoid (biphasic), and desmoplastic. 1 Although epithelioid mesotheliomas most frequently present a tubulopapillary, adenomatoid (microglandular) or solid pattern, on rare occasions, they may present other histologic patterns, including deciduoid, [2][3][4] clear cell, 5,6 adenoid cystic, 7 pleomorphic, 8,9 small cell, 10,11 rhabdoid, 12 glomeruloid, 13 signet-ring cell 14,15 and oncocytoid. 16 Some of these patterns, such as the pleomorphic, however, have not been well defined.…”

“…This is apparent in a recent publication in which it was suggested that pleomorphic mesothelioma should be regarded as a sarcomatoid pattern, rather than a subtype of diffuse epithelioid malignant mesothelioma as it is currently considered in the WHO Classification. 9 In a review of the literature, I was able to find only three publications that focused primarily on pleomorphic mesothelioma, 8,9,17 one of which was a case report. To my knowledge, with the exception of that single case report, no other study has been published in which the immunophenotype of a pleomorphic mesothelioma was investigated.…”

Epithelial–mesenchymal transition in malignant mesothelioma

“…Further larger studies should investigate the possible correlations of the epithelial-mesenchymal transition markers with survival among the histological variants of epithelioid malignant mesothelioma (and the pleomorphic subtype, in particular) and also with the presence/absence of lymph node metastasis. 29 Overall, the demonstration of epithelial-mesenchymal transition in malignant mesothelioma is a suitable model for studying this process in vivo. One of the most important arguments against the existence of epithelial-mesenchymal transition in human solid tumors is that it has not been identified in most cases.…”

“…25 Several authors reported the association between malignant mesothelioma subtype and patient prognosis. [25][26][27][28][29] Indeed, a purely epithelioid histology involved the longest survival, a purely sarcomatoid histology the worst, and a biphasic pattern an intermediate survival. [26][27][28] This study was conducted to investigate the role of epithelial-mesenchymal transition in malignant mesothelioma histological subtyping.…”