CDKN2A and skin squamous cell carcinoma: Ultraviolet light is the major oncogenic stimulus of cSCC and the % of mutations conforming to an ultraviolet signature (C-T or G-A transitions) of our candidate drivers ranged from 79.7% in CDKN2A to 30.4% in HRAS (Fig. 3b), with mutations in both TGFβ receptor genes lying within this range.