NOTCH1 and cutaneous squamous cell carcinoma: Genes that are recurrently mutated in cutaneous squamous cell carcinoma are also frequently mutated in sun-exposed epidermis (Fig. 2c) and the location of mutations within the NOTCH1 gene in our samples closely parallels that seen in cutaneous squamous cell carcinoma (Fig. 2d, e; Supplementary Fig. 3).