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The galactose oxidase-Schiff (GOS) reaction detects D-galactose-β-[1,3]-N-acetyl-D-galactosamine. This is a T-antigen expressed in mucus from malignant cells and colonic mucosa adjacent to cancer but not in normal mucosa. Previous studies using a qualitative GOS assay proved to be of limited value for the detection of colorectal neoplasia. We used a newly developed quantitative GOS assay to determine its potential as an early detection biomarker for colorectal cancer. We completed a multi-center, prospective, cross-sectional cohort validation study consisting of 70 normal controls, 23 high-risk normal patients (polyp history or family history of colorectal cancer (CRC) with currently normal colonoscopy), 137 patients with adenomatous polyps, and 69 with colorectal cancers. Prior to colonoscopy, two samples of stool were collected via a rectal exam: one for FOBT, and one for GOS. The area under the ROC curve (AUC) for detecting colonic adenomas and cancer for normal colons, computed with logistic regression was 0.69 for GOS, 0.62 for FOBT, and 0.73 for GOS combined with FOBT. Adding GOS to FOBT did not significantly change the ROC of FOBT alone. GOS does not appear to be a suitable marker of colorectal neoplasia.