As a result of spontaneous loss of the WT Nf1 and p53 alleles, cisNf1+/–p53+/– (hereafter referred to as cisNP) mice develop a variety of sarcomas including MPNST (cisMPNST) between 3 and 7 months of age. The gene discussed is NF1; the disease is malignant peripheral nerve sheath tumor.