Not our lane
By Jennifer Weiss, MD, MS
In 2021, the AGA published a clinical practice update on chemoprevention for colorectal neoplasia that advises clinicians to use low-dose aspirin to reduce colorectal cancer (CRC) incidence and mortality in average-risk individuals who are (1) younger than 70 years with a life expectancy of at least 10 years, (2) have at least a 10% 10-year cardiovascular disease (CVD) risk, and (3) are not at high risk for gastrointestinal bleeding.1 As gastroenterologists, we may see average-risk patients only at the time of their screening or surveillance colonoscopies, and I wonder if we should be taking the lead in prescribing/recommending aspirin for CRC chemoprevention in these patients. To answer this question, I will review three main concerns: (1) issues with the overall strength of the evidence on the effectiveness of aspirin to reduce CRC incidence and mortality, (2) determining an individual’s long-term CVD risk and life expectancy may be outside of a gastroenterologist’s purview, and (3) the potential for serious gastrointestinal bleeding is dynamic and requires continual review.
Studies examining the effects of aspirin on CRC incidence and mortality have limitations and mixed results. Many of the randomized controlled trials have primarily been secondary analyses of studies with primary CVD endpoints. When examined individually some studies show no significant reduction in CRC risk such as the Women’s Health Study (at 10 years of follow-up), the Swedish Aspirin Low-Dose Trial, and the UK-TIA Aspirin Trial, while some meta-analyses have shown a decrease in CRC incidence and mortality.2 One reason for this discrepancy may be varying lengths of follow-up across studies. In addition, we do not yet know the optimal aspirin dose or duration of therapy. The protective effect of aspirin on CRC incidence and mortality in average-risk individuals is mostly seen after 10-20 years of follow-up. This is relevant to the first part of the AGA clinical practice update recommendation that refers to individuals with a life expectancy of at least 10 years. The second part of the recommendation includes individuals with a 10-year CVD risk of at least 10%. As gastroenterologists, we may see these patients only two to three times over a 10-20 year period and only for their screening/surveillance colonoscopy. I would argue that we are not in the best position to address changes in life expectancy and 10-year CVD risk status over time and determine if they should start or continue taking aspirin for CRC chemoprevention.
The United States Preventive Services Task Force is also reexamining their previous recommendations for aspirin for primary prevention of cardiovascular disease. The 2016 guidelines recommended initiation of low-dose aspirin for primary prevention of CVD and CRC in adults aged 50-59 years who have a 10% or greater 10-year CVD risk and at least a 10-year life expectancy (Grade B). The current draft recommendations state that aspirin use for the primary prevention of CVD events in adults aged 40-59 years who have a 10% or greater 10-year CVD risk has a small net benefit (Grade C) and that initiating aspirin for the primary prevention of CVD events in adults aged 60 years and older has no net benefit (Grade D). They also state that, based on longer-term follow-up data from the Women’s Health Study and newer trials, the evidence is inadequate that low-dose aspirin use reduces CRC incidence and mortality.3 Because of these moving targets, we may also find ourselves walking back the AGA clinical practice update recommendations in the future.