Detection of codon 61 point mutations of the K-ras gene in lung and colorectal cancers by enriched PCR.

Mutation of the Kirsten ras (K-ras) gene is one of most common alterations in solid tumors including lung and colorectal cancers. We developed new enriched PCR-RFLP assay to detect mutations of K-ras codon 61 at the 1st and 2nd letters and non-enriched PCR-RFLP assay to detect the 3rd letter mutation. One mutant allele among 10(3) wild-type alleles was detected by enriched PCR-RFLP assay, while one mutant in 10 wild-type alleles was detected by non-enriched PCR-RFLP assay for codon 61 3rd letter. We then examined K-ras codon 12, 13 and 61 mutations in lung and colorectal cancers using these assays. K-ras codon 12 mutation was detected in 10 of 109 (9%) lung cancer and 19 of 83 (23%) colorectal cancer cases. K-ras codon 13 mutation was detected in 2 of 83 (2%) colorectal and 0 of 109 NSCLC cases, respectively. There was no K-ras codon 61 mutation in either type of cancer. Our results demonstrate that enriched PCR-RFLP is a sensitive assay to detect K-ras codon 61 mutation, however, it was extremely rare in lung and colorectal cancers, suggesting organ-specific pathways in mutagenesis of the ras gene family.