Davidson B, et al. - The diagnostic role of BAP1 in effusion cytology was investigated via analyzing effusions (n = 258), consisting of 53 malignant mesotheliomas and 205 other cancers, the majority carcinomas (62 breast, 60 ovarian, 31 lung, 51 carcinomas of other origin, 1 melanoma), for BAP1 expression using immunohistochemistry. Frequent loss of BAP1 in malignant mesothelioma effusions was noted. In the vast majority of metastatic carcinomas, BAP1 is retained. Findings thereby support the role of BAP1 as a highly sensitive and specific marker for malignant mesothelioma in serous effusions. Researchers thus recommend inclusion of this test in all specimens in which this diagnosis is considered.