[Detection of point mutation of K-ras gene codon 12 in biliary tract and ampullary carcinoma by modified two-step polymerase chain reaction].

The point mutation of K-ras gene at codon 12 was investigated in 11 cases of gall bladder carcinoma, 10 cases of extrahepatic bile duct carcinoma, 2 cases of intrahepatic bile duct carcinoma, and 4 cases of ampullary carcinoma by modified two-step polymerase chain reaction which employed paraffin embedded materials. The results revealed that there were point mutations in 6/11, 10/10, 2/2, and 4/4, respectively. Judging from the ratio of density of wild and mutant band, not all cancer cells in the tissue section contained the mutation. So it was suggested that the normal cells were initiated for the malignant transformation by ras gene mutations and then, selection might occur against cells containing ras mutations during progression of the tumor. Modified two-step polymerase chain reaction was markedly useful for detecting mutation even at low frequency among tumor cells.