NOTCH1 and skin squamous cell carcinoma: Considering the ratios of non-synonymous to synonymous mutations, the authors identified five potential driver genes that were positively selected and were associated with clonal cell expansions, NOTCH1, NOTCH2, NOTCH3, TP53 and FAT1. About 20% of normal skin cells were estimated to have NOTCH1 mutations, a mutation that is commonly found in squamous cell carcinomas of the skin (Wang et al. 2011; Pickering et al. 2014).