To determine if mice with germline Bap1 heterozygous mutations are prone to the development of mesothelioma without exposure to asbestos fibers or other carcinogenic environmental agents, Kadariya et al. monitored spontaneous tumor development for up to 31 months in three genetically engineered mouse models (GEMMs) with different heterozygous inactivating Bap1 mutations [5]. The gene discussed is BAP1; the disease is neoplasm.