CDKN2A and skin sarcoma: All AID-Cre-YFP KrasG12DArf −/− mice developed rapidly progressive papillomas and by 13 wks, 66% of AID-Cre-YFP KrasG12DArf −/− mice (n = 3) developed cutaneous sarcomas (Figure 7A), while AID-Cre-YFP Arf −/− control mice remained disease-free (Figure 7B).