Peritoneal Mesothelioma Pathology

In this article, we will discuss Malignant Peritoneal Mesothelioma Pathology (Part-I). So, let’s get started.

Histology and Immunohistochemistry

Histologically. MPM is divided into epithelioid, sarcomatoid, and biphasic subtypes. Among these. epithelioid
is the most common, representing 75-90% of reported cases, and is associated with the best prognosis, as mentioned above. Approximately 25% of MPMs are biphasic, while the sarcomatoid subtype is extremely rare. The epithelioid subtype is composed of cells that resemble normal mesothelial cells in a predominantly tubulopapillary or trabecular pattern with uncommon mitotic figures. The biphasic subtype consists of both epithelioid and sarcomatoid elements, with each component contributing at least 10% of the overall histology. The sarcomatoid subtype is composed of
tightly arranged spindle cells with sporadic malignant osteoid, chondroid or muscular features. The prognosis of biphasic and
sarcomatoid subtypes is significantly worse, similar to that of the corresponding pleural mesothelioma variants. The diagnosis of MPM based entirely on histologic patterns may be challenging thus, immunohistochemical panels are
usually used and can provide the more sensitive and specific information needed for an accurate diagnosis. In addition, there is increasing interest in using markers relatively tissue-specific transcription factors. Furthermore, the optimal immunohistochemical panel for distinguishing MPM from ovarian serous tumors remains to be clearly defined.

There is a general consensus that EMA, calretinin, CK5/6, Wilms tumor 1 (WT-1), HBME-1, thrombomodulin, podoplanin, mesothelin, and D2-40 are immunoreactive in MPM. However, WT1, D2-40, calretinin and cytokeratin 5/6 can also be positive in the majority of serous carcinomas. On the other hand, TTF1, CEA, Ber-Ep4, LeuM1, B72.3, MOC31 and cluster of differentiation (CD) 15 are commonly
expressed in adenocarcinoma rather than mesothelioma. Overall it is recommended to use at least two mesothelioma markers and two carcinoma markers.

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