Pleural diffuse mesothelial lesions: A challenge for pathologists

Malignant mesothelioma (MM) is a highly aggressive tumor deriving from the mesothelial cells normally lining the body cavities.  Histologically, MM is classified in three major histopathological patterns, such as epithelioid, sarcomatoid and mixed type. It is well known that the diagnosis of MM can be very challenging, especially in small bioptic fragments or cytological specimens. The most common diagnostic pitfalls involve the distinction between primary epithelioid MM and metastatic adenocarcinoma as well as that between reactive epithelial/fibrous benign proliferations and MM. Recently, a pathologist’s panel suggested new practical strategies and recommendations for the MM diagnosis, regarding the interpretation of histo-cytological features and the composition of appropriate immunohistochemical algorithm. Finally, according to the updated international guidelines, morphological data require a careful clinico-pathological correlation to achieve an accurate diagnosis of pleural lesions.