As reported before, cis Nf1+/−;Tp53 +/− (NPcis) mice are naturally predisposed to a number of solid malignancies, which typically form ~3–5 months after birth: 77% will develop soft tissue sarcomas—of which 60–65% are MPNSTs, 20% malignant Triton tumors, 10% rhabdomyosarcomas, 10% leiomyosarcomas and fibrohistiocytomas, 14% lymphomas, 8% carcinomas, and 1% neuroblastomas [21,22,23]; astrocytomas have also been reported [24,26]. This evidence concerns the gene TP53 and leiomyosarcoma.