K-Ras is frequently activated by mutations in cancers of the lung, colon, pancreas and biliary tract, whereas activated mutations of H-Ras and N-Ras are much rarer and mainly confined to urinary tract tumours in the case of H-Ras, and leukemia, melanoma and neuroblastoma in the case of N-Ras[42]. This evidence concerns the gene HRAS and leukemia.