Loss of expression of BRCA1 associated protein (BAP1) or methylthioadenosine phosphorylase (MTAP) or homozygous deletion of cyclin‐dependent kinase inhibitor 2A (CDKN2A) (p16) by FISH helps to distinguish reactive mesothelial cells from malignant pleural mesothelioma. This evidence concerns the gene CDKN2A and malignant pleural mesothelioma.