TP53 and diffuse large B-cell lymphoma: Only 25 % (2/8) of the DLBCL PDX models harbored inactivating TP53 mutations whereas 75 % (6/8) of tumors exhibited copy number alterations of TP53 or its upstream modifier, CDKN2A, consistent with the reported incidence and type of p53 pathway alterations in primary DLBCL.