TP53 and neoplasm: Following MYC inactivation, SA-beta-galactosidase positivity in MYC p19ARF−/− tumor sections was much lower than in MYC or MYC p53−/− tumor sections (12% in MYC p19ARF−/−versus 68% in MYC, p = 0.002, 49% in MYC p53−/− versus 68% in MYC, n.s.)(Figure 5A).