The Latest on Low-Dose Aspirin for Colorectal Cancer Prevention
Douglas K. Rex, MD, MASGE, reviewing Nafisi S, et al. Am J Gastroenterol 2024 Feb 1.
Many studies have shown that long-term use of aspirin and other nonsteroidal anti-inflammatory drugs reduces the risk of colorectal adenomas and colorectal cancer. However, the evidence varies, and in 2022, the U.S. Preventive Services Task Force concluded that there is inadequate evidence that low-dose aspirin reduces colorectal cancer (CRC) incidence or mortality.
A new population- and registry-based study from Norway included nearly 2.2 million persons aged 50 years or older living in Norway for at least 6 months during the interval 2004 to 2018. Of these individuals, 26.5% were low-dose aspirin users, and 38,577 (1.8%) developed CRC. Current use of low-dose aspirin versus never having used aspirin was associated with a 13% reduction in overall CRC risk, a 21% reduction in metastatic CRC, an 11% reduction in regionally metastatic CRC, and a 7% reduction in localized CRC. The overall reduction was 9% for use <3 years, 15% for use ranging from ≥3 and <5 years, and 16% for ≥5 years. Low-dose aspirin was effective in both sexes, younger and older patients, and in both the proximal and distal colon and rectum.
In Norway, low-dose aspirin is primarily available in 75-mg and 160-mg doses; the 160-mg dose was more effective in reducing CRC (19% vs 12% reduction). Past use of low-dose aspirin was less effective, and the benefits appeared to diminish as the length of time since stopping aspirin increased.
COMMENT
One of the most common questions asked in the recovery room after colonoscopy is "What can I do to prevent polyps?" Although controversial, it’s fair to say that substantial evidence supports a benefit for low-dose aspirin use, particularly daily use for at least 5 years, and the reduction in CRC risk is in the order of 10% to 15%. At the same time, it is appropriate to remind patients of the bleeding risk and that the U.S. Preventive Services Task Force has backed off on the benefits of low-dose aspirin as a primary cardiovascular prophylactic. I often advise patients to discuss the issue with their primary care physician or cardiologist in the context of their cardiovascular risk and remind them that no chemoprevention for CRC currently replaces the value of surveillance colonoscopy.
Note to readers: At the time we reviewed this paper, its publisher noted that it was not in final form and that subsequent changes might be made.
Douglas K. Rex, MD, MASGE
CITATION
Nafisi S, Støer NC, Veierød MB, et al. Low-dose aspirin and prevention of colorectal cancer: evidence from a nationwide registry-based cohort in Norway. Am J Gastroenterol 2024 Feb 1. (Epub ahead of print) (https://doi.org/10.14309/ajg.0000000000002695)
COMMENT
This study affirms important principles for FIT screening. First, cancers detected by FIT remain in an early stage during subsequent screening rounds. Further, increasing the cutoff level of hemoglobin for positive test results reduces sensitivity but does not shift the fraction of detected cancers substantially toward later-stage CRC. Thus, programs can adjust the cutoff to levels appropriate for their colonoscopy resources, and the detected cancers will be in an early stage across a range of hemoglobin thresholds for positive tests.