Analysis of K-ras, APC, and beta-catenin in aberrant crypt foci in sporadic adenoma, cancer, and familial adenomatous polyposis.

BACKGROUND & AIMS: We have previously shown that aberrant crypt foci (ACF) are the putative precursor lesions of colorectal adenomas and subsequent cancer in humans using magnifying endoscopy. The present study was designed to investigate these genetic alterations in ACF biopsy specimens from normal subjects, familial adenomatous polyposis (FAP) or sporadic patients.

METHODS

The non-FAP cases included 34 normal subjects, 35 colorectal adenoma patients, and 19 colorectal cancer patients; there were 4 FAP patients. Biopsies were performed on ACF by magnifying endoscopy. K-ras mutations were analyzed by 2-step polymerase chain reaction and restriction fragment length polymorphism, APC mutations by in vitro-synthesized protein assay, and beta-catenin mutations by direct sequencing. Full-length APC and beta-catenin were detected by immunofluorescence.

RESULTS

In non-FAP cases, K-ras mutations were detected in 82% (89/106) of nondysplastic ACF and 63% (17/27) of dysplastic ACF. APC mutation and beta-catenin accumulation were not detected in non-FAP ACF, whereas in adenoma of these patients, positivity of APC mutation and beta-catenin accumulation were 78% (24/31), and that of K-ras mutation was 65% (20/31). FAP patients showed K-ras mutations in only 13% (1/8) of dysplastic ACF, which is the predominant form of ACF found in FAP. In FAP patients, somatic APC mutations were found in 100% of dysplastic ACF, as they are in adenoma. The frequency of K-ras mutations was 73% (8 of 11) in FAP adenoma.

CONCLUSIONS

The data suggest that in sporadic colorectal carcinogenesis, assuming the biological implication of ACF as a precursor of adenomas, there is a route where K-ras mutation mainly occurs during the formation of ACF, which then become adenomas wherein APC mutation occurs. In FAP, however, somatic mutation of APC predominantly occurs during ACF formation, followed by K-ras mutation.