Some drugs may reduce positive predictive value of screening for colorectal cancer

New research published in the prestigious journal Gastroenterology indicates that the positive predictive value of the faecal immunochemical test (FIT) in screening for colorectal cancer may be reduced by treatment with aspirin and oral anticoagulants. In the research, people aged 50–74 years with a positive result from a FIT (>15μg hemoglobin/g feces) and subsequent colonoscopy (reference standard) were studied, and users of the target medications (regular aspirin, warfarin, or direct-acting oral anticoagulants) were compared to non-users who were matched according to age, sex, screening center, and screening round. Among 4908 eligible participants, 1008 used aspirin, 147 used warfarin, 212 used DOACs, and 3541 were non-users. Cancer was detected in 234 individuals and advanced adenomas in 1305 individuals. The positive predictive value (PPV) was 3.8% for aspirin users vs 6.4% for matched non-users (P=.006); the PPV for advanced adenoma in aspirin users was 27.2% vs 32.6% for matched non-users (P=.011). For DOAC the PPV for CRC was 0.9% in users vs 6.8% in matched non-users (P=.001); the PPV for advanced adenoma in DOAC users was 20.5% vs 32.4 % in matched non-users (P=.002). There was no significant difference in PPVs for CRC or advanced adenoma in warfarin users compared to non-users. This information casts a new light over large scale screening efforts to detect colorectal cancer.