Immunocytochemical studies on PF cell blocks allow: (a) to distinguish mesothelioma from reactive mesothelial proliferations (e.g. loss of BAP1 nuclear expression, complemented by the demonstration of p16 deletion using fluorescence in situ hybridization, indicate mesothelioma); (b) to separate mesothelioma from adenocarcinoma (e.g. calretinin, CK 5/6, WT-1 and D2-40 are markers of mesothelioma, whereas CEA, EPCAM, TTF-1, napsin A, and claudin 4 are markers of carcinoma); and (c) to reveal tumor origin in pleural metastases of an unknown primary site (e.g.
Calretinin and cytokeratin 5 were used for reactive mesothelial cells and Wilms tumor 1, thyroid transcription factor 1, CDX2, and estrogen receptor were used to confirm the adenocarcinoma cells.
Antibodies against calretinin represent an established, powerful and reliable immunohistochemical marker in the differential diagnosis between mesothelioma and adenocarcinomas.
In contrast, the "AP2-like" sequence does not play such a role in regulation of the CR gene transcription in adenocarcinoma and mesothelioma cancer cells.
We conclude that calretinin is expressed by most undifferentiated colorectal adenocarcinomas, but only by a limited number of cells in well-differentiated tumors.