PTPRC and histiocytic sarcoma: We also observed that 2% of hTS/Ink4a/Arf−/− mice spleens and lymph nodes affected with lymphoma also presented histiocytic sarcoma (Fig. 2A- c, d and lymph nodes in 2A- g, h) as defined by mutually exclusive staining of CD45R and Mac-2 (Fig. S3C).