DETECTION OF K-RAS MUTATION IN COLONIC EFFLUENT SAMPLES FROM PATIENTSWITHOUT EVIDENCE OF COLORECTAL-CARCINOMA

Background: K-ras gene mutation appears in more than 50% of patients w ith colon tumors. Both its frequency and early appearance may qualify this mutation as a potential biomarker. To enable early detection of m utant K-ras alleles, we had previously developed a sensitive polymeras e chain reaction (PCR)-based assay, i.e., enriched PCR, which enables detection of one mutant K-ras allele present within 10 000 normal alle les. Using the enriched PCR, we were able to detect mutant K-ras allel es in ''normal-appearing'' colonic mucosa in patients with colorectal cancer, Purpose: A study was initiated to determine whether mutant K-r as alleles could be identified in colonic effluent samples of patients who may be at risk to develop colorectal cancer. Methods: Over 9 year s, colonic effluent samples were collected prior to routine colonoscop y from 39 patients who were apparently free of colorectal cancer. Thes e samples were collected from patients with a family history of colore ctal cancer (n = 7), adenomatous polyps (n = 7), previously resected c olorectal cancer (n = 5), inflammatory bowel disorders (n = 13), norma l colonoscopic examination (n = 6), and familial adenomatous polyposis (n = 1). All of the samples were double coded and analyzed for K-ras gene mutation. Results: Of the 39 patients, seven were found to harbor mutant K-ras codon 12 alleles. Mutations were found in patients with a family history of colorectal cancer (three of seven), adenomatous po lyps (one of seven), previously resected colorectal carcinoma (two of five), and familial adenomatous polyposis (one of one). In one case, e ffluent was found to harbor a mutant K-ras allele 4 years before the p atient was diagnosed with colorectal cancer. Conclusions: (a) Effluent samples contain enough DNA to be detected with enriched PCR. Such sam ples may well be representative of the entire colon in general as oppo sed to a localized area such as that usually analyzed during colonosco py. (b) K-ras gene mutation can be identified in routinely obtained co lonic: washings of patients who are at risk of developing colorectal c ancer. Such mutations were absent in patients with inflammatory bowel disorders and in those who had undergone normal colonoscopic examinati ons. Detection of K-ras mutation in colonic washings may assist in ide ntifying patients who may be at high risk for developing adenocarcinom a of the colon. Implications: The ability to examine colonic effluents provides a powerful and convenient source of sampling and may be adap ted for future large-scale screening.