A phenotypic change of small intestinal epithelium to colonocytes in smallintestinal adenomas and adenocarcinomas

OBJECTIVE: Using a novel monoclonal antibody (mAb Das-1) that specifically reacts with colon epithelium, we examined if there is a phenotypic change o f small intestinal enterocytes toward colonocytes in small intestinal neopl astic tissue. METHODS: Tissue sections of the small intestine consisting of adenomas (n = 20, five with histories of familial polyposis), adenocarcinomas (eight pri mary and one metastatic from colon), carcinoids (n = 2), and hyperplastic p olyps (n = 3) were examined by a sensitive immunoperoxidase assay using mAb Das-1 (IgM isotype). Normal jejunal (n = 10) and colonic (n = 10) biopsy s pecimens were also included as additional controls. RESULTS: mAb Das-1 reacted with normal colonic epithelium but not with jeju nal mucosa. However, mAb Das-1 reacted strongly with each of the five adeno mas (100%) from patients with histories of familial polyposis, but only fiv e of 15 (33%) of the adenomas from nonfamilial polyposis patients, and each of the eight (100%) adenocarcinomas of the small intestine (p < 0.001). Th e reactivity with the adenomas from nonfamilial polyposis patients was very focal. whereas in the adenomas with familial polyposis the reactivity was more extensive. Each of the eight carcinomas reacted strongly with mAb Das- 1. Adjacent normal small intestinal mucosa did not react. Hyperplastic poly ps and the carcinoids did not react with mAb Das-1. CONCLUSION: These data demonstrate a phenotypic change in small intestinal epithelium toward the colonic phenotype, particularly in familial polyposis and in adenocarcinomas. mAb Das-1 may be clinically useful in identifying small intestinal adenomas with "high risk" for malignancy, such as in famil ial polyposis.