The histopathological diagnosis of pleural biopsies is difficult and may require FISH (fluorescent in situ hybridization) of the CDKN2A locus and immunohistochemistry for p16 and BAP1 (11) when invasion is not clearly demonstrated based on the histology, and to confirm the diagnosis of mesothelioma in pleural effusions. The gene discussed is CDKN2A; the disease is Pleural effusion.