Recent attention has been drawn to the diagnostic potential of tests based on shed colonic
tumor markers.
Adnab-9 monoclonal antibody raised against neoplastic, potentially premalignant colonic
adenomas recognizes a marker in colonic effluent or tissue which correlates with the presence of
tumors or risk of
colorectal cancer. The origin of this
antigen and optimal collection of colonic effluent were investigated by
enzyme-linked
immunosorbent assay and Western blotting. Mean
Adnab-9 binding in effluent samples from
colorectal cancer patients even after resection is high as compared with that in normal subjects (P < 0.05). Effluent samples are best collected in the morning hours.
Antigen proteolysis may be significant depending on the site and timing of effluent collection, but breakdown products are reactive. Tissue and effluent
Adnab-9 binding at any one anatomic site of collection appear to correlate (r = 0.88, P = 0.01). The
Adnab-9 antigen is constitutively expressed at low levels throughout the distal bowel and localized to the deepest regions of the mucosal crypts. Other than meconium, no significant levels of binding are found in other body fluids. This
antigen is specific for the gastrointestinal tract, its binding in conveniently collected effluent samples correlates with tissue content, and the
antigen is constitutively expressed in the crypts of the distal small bowel and colonic mucosa.