Which marker is included in the Mesothelioma immunohistochemistry panel?

• A. Calretinin
• B. CK5/6
• C. PanCK
• D. CEA

Answer: (A)

Calretinin is a classic mesothelial marker used in immunohistochemistry panels to identify mesothelioma. Tumor cells in epithelioid mesothelioma typically show strong calretinin staining, which supports a mesothelial origin. In contrast, metastatic adenocarcinomas to pleura or peritoneum usually lack calretinin. This contrast helps distinguish mesothelioma from adenocarcinoma when morphology is not definitive.

Other markers have different roles: CK5/6 can be positive in mesothelioma but isn’t as specific, since it can appear in other tumor types as well. PanCK confirms epithelial nature but doesn’t differentiate mesothelioma from carcinoma. CEA is commonly expressed in many adenocarcinomas and is usually negative in mesothelioma, which helps exclude adenocarcinoma but isn’t a positive indicator for mesothelioma on its own. Thus calretinin is the best-fitting marker listed for inclusion in the mesothelioma panel.