Of the nine p16−/− tumors, two were detected in the mammary gland and were highly composed of lymphoma cells, as evidenced by their lymphocyte-like morphology, positivity for CD45 and CD31 by FACS analysis and negativity for Cdh1, an epithelial cell marker, by IHC (Supplementary Figure S2A, S2C and S2E). This evidence concerns the gene PECAM1 and lymphoma.