KRAS and cancer: Furthermore, for two of the mutation sets–KRAS, BRAF and NRAS (Supplementary Fig. 21); and APC and CTNNB1 (Supplementary Fig. 22)—there was significant heterogeneity across cancer types in terms of the number of mutations in each gene with evidence of preferential selection (selection above at least one other mutation in the set) (Fisher test, q = 2.2 × 10−3, 7.2 × 10−7, respectively), supporting a model where gene-specific effects on selection vary across cancer types.