Thymic lymphomas derived from 53BP1−/−p53−/− mice fall into two distinct cytogenetic categories: those characterized by aneuploidy that largely resemble equivalent tumors from p53−/− mice (Liao et al., 1998) and those without aneuploidy that harbor clonal translocations thought to arise from DSB repair intermediates that accumulate as a result of abortive antigen receptor gene-rearrangements and progress into oncogenic translocations when p53-dependent apoptotic responses are ablated (Difilippantonio et al., 2008, Morales et al., 2006, Ward et al., 2005). This evidence concerns the gene TP53 and lymphoma.