To assess if there was a selective pressure for the loss of the wild type allele of ESPL1 during lymphoma progression in mice, real-time quantitative PCR analysis was employed to determine the status of the wild-type ESPL1 allele in ESPL1+/hyp, p53−/− and ESPL1+/hyp, p53+/− tumors. Here, TP53 is linked to lymphoma.