BAP1 and Ascites: Another study,19 which comprises 147 pleural and peritoneal effusions including mesothelioma, adenocarcinoma, and benign mesothelial hyperplasia, investigated the loss of BAP1 expression for the diagnosis of mesothelioma by immunohistochemistry showed that loss of BAP1 occurs in 76.5% of the cell block samples and 47.5% of the biopsies in mesothelioma.