Three-Year Interval for the Multi-Target Stool DNA Test for Colorectal Cancer Screening: A Longitudinal Study

Data supporting the clinical utility of multi-target stool DNA (mt-sDNA) at the guideline-recommended 3-year interval have not been reported. Between April 2015 and July 2016, candidates for colo-rectal cancer screening whose providers prescribed the mt-sDNA test were enrolled. Participants with a positive base line test were recommended for colonoscopy and completed the study. Those with a negative baseline test were followed annually for 3 years. In year 3, the mt-sDNA test was repeated and colonoscopy was recommended independent of results. Data were analyzed using the Predictive Summary Index (PSI), a measure of the gain in certainty for dichot-omous diagnostic tests (where a positive value indicates a net gain), and by comparing observed versus expected colorectal cancers and advanced precancerous lesions. Of 2,404 enrolled subjects, 2,044 (85%) had a valid baseline mt-sDNA result [284 (13.9%) positive and 1,760 (86.1%) negative]. Following participant attrition, the year 3 inten-tion to screen cohort included 591 of 1,760 (33.6%) subjectswith valid mt-sDNA and colonoscopy results, with no colorectal cancers and 63 advanced precancerous lesions [22 (34.9%) detected by mt-sDNA] and respective PSI values of 0% (P = 1) and 9.3% (P = 0.01). The observed 3-year colorectal cancer yield was lower than expected (one-sided P = 0.09), while that for advanced precancerous lesions was higher than expected (two-sided P = 0.009). Repeat mt-sDNA screening at a 3-year interval resulted in a statistically significant gain in detection of advanced pre-cancerous lesions. Due to absence of year 3 colorectal cancers, the PSI estimate for colorectal cancer was under-powered and could not be reliably quantified. Larger studies are required to assess the colorectal cancer study findings.