Aspirin, anticoagulants up rate of false positives with FIT for colorectal cancer

By Will Boggs MD

NEW YORK (Reuters Health) - 7/2/2019

Regular use of aspirin or anticoagulants reduces the positive predictive value (PPV) of fecal immunochemical testing (FIT) for detecting colorectal cancer and advanced adenomas, researchers from Norway report.

"Despite our findings, we do not recommend cessation of any antithrombotic agents at time of fecal sampling due to the risk of thromboembolic events," Dr. Kristin Ranheim Randel of the University of Oslo and the Cancer Registry of Norway told Reuters Health by email. "However, screening participants who use direct-acting oral anticoagulants (DOACs) should be informed that they may have an increased risk of a false-positive result."

FIT for occult blood is the most frequent colorectal-cancer screening tool worldwide. Colonoscopy is recommended for follow-up of a positive FIT result, but the cost-effectiveness of such screening relies on the PPV of FIT.

Dr. Randel's team used data from a large colorectal cancer screening trial in Norway to evaluate the impact of aspirin, warfarin and DOAC use on the PPV for colorectal cancer and advanced adenoma following a positive FIT result.

Among more than 4,900 individuals included in the study, there were 1,008 aspirin users, 147 warfarin users, 212 DOAC users and 3,541 nonusers. Overall, colorectal cancer was diagnosed in 5.3% of nonusers and 3.4% of users, and advanced adenoma was diagnosed in 28.4% of nonusers and 25.8% of users.

In an analysis of individuals matched by age, sex and other variables, the PPV for colorectal cancer and for advanced adenoma was significantly lower for aspirin users (3.8% and 27.2%, respectively) than for nonusers (6.4% and 32.6%), the researchers report in Gastroenterology, online January 25.

Similarly, the PPV for colorectal cancer and for advanced adenoma was significantly lower for DOAC users (0.9% and 20.5%, respectively) than for matched nonusers (6.8% and 32.4%). In the matched analyses, the PPVs for colorectal cancer and advanced adenoma did not differ significantly between warfarin users and nonusers.

In the unmatched analyses, the PPVs for colorectal cancer and advanced adenoma were similar in aspirin and warfarin users but lower in DOAC users, compared with nonusers.

"Although we found a lower predictive value for colorectal cancer and advanced adenoma in DOAC users than in nonusers, this needs to be confirmed in other studies," Dr. Randel said. "If our results are confirmed, they may be particularly relevant in screening programs which include an intake interview ahead of colonoscopy. A possible approach could be to repeat the FIT test without DOAC, after careful discussion with the screenee."

SOURCE: Gastroenterology 2019.

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