Aspirin Not Effective in Reducing the Risk of Colorectal Cancer


Synopsis: In the only available RCT, low-dose aspirin was not effective in reducing the risk of colorectal cancer.

Source: Sturmer T, et al. Ann Intern Med 1998;128: 713-720.

The use of aspirin and other nonsteroidal anti-inflammatory drugs and their potential to reduce colorectal cancer has been actively studied. The weight of the evidence based purely on the number of positive papers suggests an effect. Ten of 11 observational studies, as well as case-control studies, have found a reduction in CRC in self-selected aspirin users. However, as we all know, observational studies can have inherent selection biases and larger randomized control trials are the gold standard. Only one RCT of this question has been performed, and none are currently active. Sturmer and colleagues from the randomized Physicians' Health Study report on the incidence of CRC with 12 years of follow-up. This report is notable in that it includes seven additional years of follow-up (post the initial report) and addresses the effects of aspirin in men after the end of the RCT. The trial involved 22,071 male physicians who were randomized to 325 mg of aspirin or placebo on alternating days. Many readers will know that the study was stopped at five years due to a 44% reduction in first myocardial infarction. The investigators subsequently monitored if the men switched to adding or stopping aspirin use for up to 12 years. The extent of follow-up was an unprecedented 99.7% of morbidity and 100% for mortality. The results were that: 1) all men in the trial had an 18% reduction in CRC compared to age-matched controls; 2) no trend for benefit with aspirin at any time interval was seen; and 3) no users, late users, or irregular users of aspirin had no difference in CRC compared to regular users.


This study once again shows the power of a large RCT to fail to confirm tantalizing results from small observational studies. Low-dose aspirin can still be strongly advocated for preventing macrovascular disease.