S531 One Versus Two Fecal Immunochemical Tests in the Detection of Advanced Colorectal Neoplasia

Introduction: The fecal immunohistochemical test (FIT) is a noninvasive means to test for colorectal cancer. Every province in Canada offers this test for individuals aged 50-74. Our goal was to determine the positive predictive value (PPV) of one versus 2 abnormal FIT in the detection of colorectal cancer and advanced adenomas. Methods: Over a 5-year period from 2020 to 2025, 84,489 completed FIT kits were received by the Newfoundland and Labrador colon cancer screening program. A participant completed 2 FIT samples and if one FIT was positive (³100 ng/ml) a colonoscopy was arranged. Data collected included demographics, colonoscopy, pathology, and quantitative FIT results. PPV of one versus 2 abnormal FITs was calculated. Results: Overall, 10,237 patients (12.1%) were positive when the FIT was analyzed; 9,203 colonoscopies were completed and 249 (2.7%) colorectal cancers were detected. The number of advanced adenomas was 26.2% and overall adenoma detection rate was 61.9%. Of the 249 cancers detected, 183 patients had both FIT samples positive while 66 patients had one FIT sample positive and one negative, 33 of 249 (13.3%) of all cancers would have been missed if only 1 FIT was analyzed. For 2,415 participants with advanced adenomas 1,194 had 1 FIT positive and 1219 had both positive. If only one FIT test was analyzed 597 advanced adenomas would have been missed. The positive predictive value (PPV) of one vs 2 positive FITs for cancer was 2.4% vs 2.7% (P value < 0.01) and the PPV for advanced adenoma was 19.8% vs 26.2% (P value < 0.01). When the first FIT was negative, the second positive FIT detected 33 additional cancers and an extra 592 advanced adenomas. Absolute FIT values were also higher for patients with 2 FIT positive compared to one FIT positive for both cancer (6,449 vs 5,337) and advanced adenomas (2,243 vs 878). Conclusion: The PPV of 2 positive FITs is superior to one positive FIT for both colorectal cancer detection as well as advanced adenomas. The second FIT detected an additional 13% of cancers. This is a significant increase in the number of cancers detected, the downside is that patients have to complete 2 FIT samples as opposed to one. Compliance with 2 samples is less than one. Similar results were noted in that more advanced neoplasia was detected with the addition of a second kit.