CDKN2B and sarcoma: We showed that spontaneously transformed murine MSCs harbour point mutations in Trp53 and/or copy number alterations in Cdkn2a and Cdkn2b. Upon inactivation of Trp53, murine MSCs transformed earlier compared to wild-type, confirming the contribution of loss of p53 to spontaneous transformation and development of sarcomas with a complex genome.