MUCOSAL ORIGIN AND SHEDDING OF AN EARLY COLONIC TUMOR-MARKER DEFINED BY ADNAB-9 MONOCLONAL ANTIBODY

Recent attention has been drawn to the diagnostic potential of tests b ased on shed colonic tumor markers. Adnab-9 monoclonal antibody raised against neoplastic, potentially premalignant colonic adenomas recogni zes a marker in colonic effluent or tissue which correlates with the p resence of tumors or risk of colorectal cancer. The origin of this ant igen and optimal collection of colonic effluent were investigated by e nzyme-linked immunosorbent assay and Western blotting. Mean Adnab-9 bi nding in effluent samples from colorectal cancer patients even after r esection is high as compared with that in normal subjects (P < 0.05). Effluent samples are best collected in the mooting hours. Antigen prot eolysis may be significant depending on the site and timing of effluen t collection, but breakdown products are reactive. Tissue and effluent Adnab-9 binding at any one anatomic site of collection appear to corr elate (r = 0.88, P = 0.01). The Adnab-9 antigen is constitutively expr essed at low levels throughout the distal bowel and localized to the d eepest regions of the mucosal crypts. Other than meconium, no signific ant levels of binding are found in other body fluids. This antigen is specific for the gastrointestinal tract, its binding in conveniently c ollected effluent samples correlates with tissue content, and the anti gen is constitutively expressed in the crypts of the distal small bowe l and colonic mucosa.