Both p53−/− and p19ARF−/− mice are predisposed for development of lymphoma (Donehower et al., 1992; Kamijo et al., 1999), and MuLV infection further accelerated lymphomagenesis in these mice as well as in wild-type mice (p value < 0.0001 for MuLV-infected p19ARF−/− versus noninfected p19ARF−/−, p value < 0.0001 for MuLV-infected p53−/− versus noninfected p53−/−, log-rank test) (Figure 1A). This evidence concerns the gene TP53 and lymphoma.