Studies On The Expression And Mutations Of K-ras Gene In Pancreatic Diseases

Pancreatic carcinoma is a highly malignant tumor, which is typically associatedwith a very poor prognosis and advanced stage at presentation. The 5-year-survivalrate is less than 5%. The early diagnosis of pancreatic carcinoma with currentdiagnostic means is extremely difficult. Mutations of 12 codon in exon 1 of K-rasoncogene are detected at a remarkably high frequency (70~100%) in pancreaticcarcinomas and believed to be a early and critical event in oncogenesis. Hyperplasticductal lesions of the pancreas are believed to represent precursors of ductaladenocarcinoma. However, the K-ras mutations were also be detected in benignpancreatic diseases and ductal hyperplasia in normal pancreas. The frequency andsignificance of this mutation in pancreatic diseases are a matter of controversy.In this study , first, we investigated the expression of P21 by immuno-histochemical method in pancreatic carcinoma, neighbouring hyperplastic ductallesions and chronic pancreatitis to identify the role of P21ras in pancreatic diseases.Second, we detected K-ras mutations in DNA obtained from paraffln-embededspecimens of pancreatic carcinoma and chronic pancreatitis by means of two-steppolymerase chain reaction (PCR) combined with restriction enzyme digestion,followed by nonradioisotopic single-strand conformation polymorphism (SSCP)analysis and by means of automated DNA sequencing. The conclusions are as follows:1.The expression level of P21 of pancreatic carcinoma and chronic pancreatitis washigher than that of normal pancreatic tissue, but the expression of P21 in ductalhyperplasia neighbouring pancreatic carcinoma was similar to that in ductalhyperplasia of chronic pancretitis. P21 ras showed a gradual stepwise increase in thefrequency of expression from normal pancreatic duct (0%), to hyperplasia duct (3 9.6%)and to atypical hyperlasia duct (78.9%). The results suggested that P2lras may play arole in the malignant transformation of pancreatic ductal cell.32.The expression level of P21ras of pancreatic carcinoma was lower than that of ductalatypical hyperplasia, which confirmed that the change of expression level of oncogeneis a early event of malignant transformation of cells. This suggested thatoverexpression of P21ras had some diagnostic value to pancreatic carcinoma.3.The frequency of K-ras 12 codon mutations increased obviously in the pancreaticcarcinoma to chronic pancreatitis (p< 0.01). So, a conclusion can be drawn that thedetection of K-ras 12 codon mutations is useful for diagnosing pancreatic carcinomaand differentiating chronic pancreatitis from carcinoma.4.The mutation pattern of K-ras 12 codon of chronic pancreatitis was GGT~GAT,GGT and CGT, which is identical to that in pancreatic carcinoma. This indicated thatchronic pancreatitis was related to pancreatic carcinoma. So, for diagnostic andtherapeutic purpose, the detection of K-ras mutations should be supplemented by thedemonstration of additional genetic alterations or clinical signs of malignancy.