Mutational Activation of H‐ras and K‐ras Genes Is Absent in N‐Nitroso‐N‐methylurea‐induced Liver Tumors in Rats

We examined mutational activation of H‐ and K‐ras genes in hyperplastic nodules and hepatocellular carcinomas induced by N‐nitroso‐N‐methylurea or diethylnitrosamine using the polymerase chain reaction, followed by dot‐blot hybridization. No mutational activation was detected in these hepatic lesions. The results indicate that low incidence of the activation of H‐ and K‐ras genes in rat liver tumors is due to the organ specificity rather than the nature of the carcinogens used.