Individuals harboring inherited heterozygous mutations of the BAP1 gene are predisposed to a spectrum of neoplasms, including malignant mesothelioma. Using genetically engineered mouse models, it was found that inactivating germline Bap1 mutations behave as potent cancer susceptibility alleles, giving rise to a variety of malignant tumor types, including occasional mesotheliomas. However, high penetrance of mesothelioma in Bap1-mutant mice required exposure to asbestos. The image depicts hematoxylin and eosin staining of a spontaneous malignant mesothelioma invading the pancreas of mouse with a germline Bap1 mutation. For details, see article by Kadariya and colleagues on page 2836.