TP53 and carcinoma: Seven of 14 (50%) carcinomas from p19 Arf+/+p53+/−, and three of 14 (21%) from p19 Arf+/−p53+/−, but only one of 12 (8%) from p19 Arf−/−p53+/− (p = 0.036) showed loss of p53. Thus, deletion of p19Arf disrupts the activation of p53 and thereby reduces selection for mutations in p53 during malignant progression.