TP53 and neoplasm: The p16INK4A immunohistochemical staining in p19ARF−/−, but not in MYC p53−/−, tumor sections was significantly reduced than in MYC tumor sections (41% in MYC p19ARF−/− versus 76% in MYC, p = 0.025; 67% in MYC p53−/− versus 76% in MYC, n.s.)(Figure 5B).