Loss of BRCA1-associated protein 1 (BAP1) expression is useful in diagnostic cytopathology of malignant mesothelioma in effusions
Background: The important diagnostic challenge facing the cytopathologist is whether a mesothelial proliferation on effusions represents a malignant mesothelioma (MM) or a benign mesothelial hyperplasia (MH). Here, we evaluated the diagnostic utility of BAP1 immunohistochemistry (IHC) in distinguishing between reactive and neoplastic mesothelial cells. Methods: In pleural and peritoneal effusions from 147 patients with diagnosed MM or with a differential diagnosis of MM and MH, the expression of BAP1 was examined by IHC on paraffin-embedded cell blocks (n = 121) and biopsies (n = 44).