DPC-4 (Smad-4) and K-ras gene mutations in biliary tract epithelium in children with anomalous pancreaticobiliary ductal union

Background/Purpose: Recent studies have found that anomalous pancreaticobiliary ductal union (APBDU) is a substantial risk factor for biliary tract cancer at a younger age. DPC-4 (Smad-4) is a new tumor suppressor gene frequently inactivated in pancreatic and bile duct adenocarcinoma. To clarify carcinogenesis in APBDU, the authors investigated possible DPC-4 and K-ras mutations in 35 pediatric patients. Methods: DNA was extracted from biliary tract epithelial cells, which were resected surgically and histologically purified using microdissection. Polymerase chain reaction (PCR) primers were designed specifically for exons 8-11 of DPC-4 (18q21.1) and exons 1-2 of the K-ras oncogene (12p12.1). DNA sequences were determined using the direct DyeDeoxy Terminator Cycle method. Results: Of 35 children, 30 had wild-type DPC-4 and K-ras genes. K-ras mutations were detected in 5 patients, 4 of whom showed epithelial hyperplasia or metaplasia. In a 12-year-old girl with adenocarcinoma arising from a choledochal cyst, K-ras and DPC-4 (homozygous deletion) mutations were identified simultaneously. Conclusions: These results suggest that carcinogenesis in the biliary tract epithelium in APBDU is accompanied by multistep genetic mutational events; K-ras gene mutation occurs early in epithelial hyperplasia or metaplasia, whereas inactivation of the DPC-4 gene accumulates late in the progression of biliary tract adenocarcinoma.