A cancer-associated mucin alteration in benign colonic polyps.

Abstract

Abstract We have recently reported that the mucin in colon cancer is different from that in the normal colon, and this difference may be detected by selective lectin binding characteristics. The lectin Dolichos biflorus agglutinin [DBA] avidly binds to the mucin found in well-differentiated goblet cells in the normal colon, but does not bind to that in the majority of colonic cancers. Conversely, the lectin peanut agglutinin (PNA) does not bind to the mucin from the normal colon, but avidly binds to that in colon cancer. Therefore, these two lectins were used to determine if cancer-associated mucin were present in benign colonic polyps. Fluorescein isothiocyanate (FITC) conjugates of Dolichos biflorus agglutinin and peanut agglutinin were applied to fixed, unstained tissue sections of 56 colonic polyps and examined by fluorescent microscopy. Focal areas were found within the polyps in which FITC-DBA labeling was diminished (compared with the normal colon) and labeling with FITC-PNA appeared. The findings are expressed as the percentage of glands per polyp labeled by FITC-PNA. The median labeling in 31 benign tubular adenomas was 7% of the glands per polyp. In 16 benign tubular adenomas ≤7 mm in diameter, only 2% of the glands per polyp were labeled, while in 15 benign tubular adenomas > 7 mm in diameter, 24% of the glands per polyp were labeled. Carcinoma in situ or invasive carcinoma was found in nine adenomatous polyps, in which 41% of the adenomatous glands were labeled by FITC-PNA. Unexpectedly, in eight hyperplastic polyps, 89% of the glands were labeled by FITC-PNA. These results indicate that among neoplastic colonic polyps, cancer-associated mucin changes are present and are more widespread in larger tubuluar adenomas, villoglandular adenomas, and adenomas containing cancer. The presence of mucin that is bound by FITC-PNA may be an indication of an increased risk of developing cancer within a colonic polyp. The finding of the cancer-associated mucin in hyperplastic polyps raises new questions about the pathogenesis of these benign, apparently nonneoplastic lesions.