CDKN2A and neoplasm: Apart from TP53, which is one of the first inactivated tumor suppressor genes, a handful of key mutations frequently found in SCC of the skin have been proposed, among them CDKN2A, NOTCH 1, NOTCH 2, FAT1 and RAS family members, involved in different cellular processes, such as cell-cycle control, squamous cell differentiation, survival and proliferation (Figure 2).