T2034 Stool DNA and Occult Blood for Detection of Colorectal Cancer: Complementary Markers

Non-apoptotic human DNA (long DNA) in stool is a discriminant marker for colorectal cancer (Gastroenterology 2000; 119:1219). Fecal long DNA may originate from either the exfoliation of dysplastic cells or from the luminal hemorrhage or exudation of leukocytes. The contribution of these potential sources long DNA in stool has not been examined. If leukocytes are the major source, then fecal human DNA and occult blood levels should correlate. If exfoliation is the major source, then fecal human DNA and occult blood should be complementary markers for colorectal cancer. AIM: To quantify and correlate human DNA and hemoglobin in stools from patients with colorectal neoplasia, and to consider a simple stool assay for cancer screening. METHODS: Subjects comprised 74 patients with colorectal cancer, 27 with adenomas >1cm, and 100 with normal colonoscopy. One stool per subject was collected in stabilization buffer before or > 1 week after colonoscopy. Fecal long DNA and occult blood were quantified in blinded fashion by real-time Alu PCR (CEBP 2006 15:1115) and the HemoQuant assay (Mayo Medical Laboratories), respectively. HemoQuant assay results are not affected by fecal storage (Ann Intern Med 1984;101:297) and could be reliably applied to archival specimens for this study. RESULTS: Fecal long DNA and occult blood showed no correlation (R2=0). At 90% specificities, long DNA testing detected 70% of colorectal cancers and 46% of adenomas while occult blood testing detected 50% and 12%, respectively. Combining these tests detected 80% colorectal cancers and 46% of adenomas at 90% specificity. For detection of colorectal cancer, AUC values were 0.82, 0.78, and 0.90 for fecal long DNA, occult blood, and combination testing, respectively (p