BAP1 and mesothelioma: Genetic testing for CDKN2A/2B loss and immunohistochemistry (IHC) for methylthioadenosine phosphorylase (MTAP) loss and BAP1 loss are currently thought to be the most reliable molecular tools for differentiating mesothelioma from other malignancies and, often most critically, from reactive mesothelial hyperplasia, which is a benign change.