N-nitroso compounds could also induce G>A transitions in codons 12 or 13 of the K-ras gene of rat colon carcinomas (Zarbl et al, 1985; Topal, 1988; Jacoby et al, 1992) or in human colonic tissue (Hughes et al, 2001; Bingham et al, 2002). This evidence concerns the gene KRAS and colon carcinoma.