CDKN2A and fibrosarcoma: We did not observe a significant increase in fibrosarcoma (3/15 (20%) hTS/Ink4a/Arf+/– vs 2/14 (14%) in Ink4a/Arf+/– mice) but 3 out of 15 hTS/Ink4a/Arf+/– mice (20%) developed histiocytic sarcoma while this tumor was not observed in Ink4a/Arf+/- mice (Fig. 1C).