<scp>HEG1</scp>, <scp>BAP1</scp>, and <scp>MTAP</scp> are useful in cytologic diagnosis of malignant mesothelioma with effusion

HEG1 is a good marker for mesothelial differentiation in effusion cytology. HD of CDKN2A is frequently observed in cell blocks from effusions of MMs, and MTAP IHC may act as a surrogate for HD of CDKN2A. Cell block analysis is recommended for effusions of unknown origins with the following methods: IHC with HEG1 and claudin 4 to validate the mesothelial origin, followed by BAP1 and MTAP IHC to confirm malignancy.