Direct sequencing analysis of exon 1 of the c-K-ras gene shows a low frequency of mutations in human pancreatic adenocarcinomas.

We have applied direct dideoxy sequencing of DNA fragments amplified in vitro by the polymerase chain reaction to the detection of mutations in exon 1 of the c-K-ras gene in human pancreatic adenocarcinomas. Four fresh frozen primary tumors, one metastatic tumor, and twelve formalin-fixed paraffin embedded tumors were analysed. Only three cases showed a possible mutation in codon 12 in a small population of cells, in contrast to the high frequency reported for this alteration with the RNAase A protection assay and allele-specific oligoxynucleotide hybridization. No major difference in sensitivity was found between DNA sequence analysis, and the latter method. Our results suggest that if c-K-ras mutations are indeed present in pancreatic adenocarcinomas at the high frequency reported by others, they must be confined to a small fraction of the cell population to escape detection by direct sequencing. Such a phenomenon would have implications for c-K-ras mutations in the pathogenesis of pancreatic adenocarcinomas.