TP53 and neoplasm: As in the p53-wild-type background, Arf knockout in RIP-Tag2; p53−/− mice resulted in a significantly increased (2.4-fold) tumor burden at 12 weeks of age compared to Arf+/+ littermates (Figure 7A; p<0.001), as well as a significant 30% increase in the number of angiogenic lesions (Figure 7C; p = 0.04) and small tumors (Figure 7D; p = 0.002) at 8 weeks of age, confirming that these effects are at least in part p53-independent.