Comparison of K-ras point mutation distributions in intraductal papillary-mucinous tumors and ductal adenocarcinoma of the pancreas

Intraductal papillary-mucinous tumors (IPMT) consist of cells with varying histologic degrees of severity and exhibit multiple tumor loci; however, whether or not these lesions exhibit the same genetic changes has not been clarified. To investigate this point, we analyzed K-ras mutations in multiple IPMT lesions from each patient enrolled in our study and compared our findings to those for patients with ductal adenocarcinoma of the pancreas (DC). Twenty IPMT specimens and 7 DC specimens were resected, microdissected and analyzed for the presence of K-ras mutations. The mutated genes were then sequenced using a genetic analyzer. K-ras mutations were observed in 80% of IPMT and 100% of DC patients. More than 2 types of K-ras mutation were observed in the main tumors of 43.8% of IPMT and 0% of DC patients. K-ras mutations in peritumoral and separated lesions were observed in 66.7% and 62.5% of IPMT patients, respectively. At least one identical mutation between the main tumor and the peritumoral or separated lesions was recognized in all of the IPMT patients with those lesions. Different mutations from those in the main tumor were observed in 40% of IPMT patients with separated lesions. The survival curve of IPMT-carcinoma patients with more than 2 types of K-ras mutation in the main tumor was better than that with one type of K-ras mutation. IPMT patients exhibit a remarkably genetic heterogeneity in main tumor and have good prognosis.