GLP-1s outdo aspirin in colorectal cancer prevention, study finds | ASCO Gastrointestinal Cancers Symposium

There is ample evidence that aspirin can lower the risk of getting colorectal cancer, although the advantages of the protection it affords have to be weighed against the added risk of gastrointestinal bleeding and other side effects. Aspirin may now have some competition in the colorectal cancer protection research department. Results shared today at a press briefing for the 2026 American Society of Clinical Oncology (ASCO) Gastrointestinal Cancers Symposium showed that the glucagon-like peptide (GLP-1) drugs that have become hugely popular as weight loss medication are 36% more effective in reducing colorectal cancer than aspirin.

The results of the head-to-head comparison with aspirin also showed that the GLP-1s were far less likely to be associated with acute kidney injury than aspirin and also came out ahead when it came to gastrointestinal bleeding and gastric ulcers. However, people taking GLP-1s were 13% more likely to experience diarrhea than those taking aspirin, a not unexpected result because diarrhea is a recognized side effect of the GLP-1s, a class that includes semaglutide, sold under the name Ozempic for diabetes and as Wegovy for weight loss.

“I think this is certainly an interesting analysis,” said Joel N. Saltzman, M.D., of the Cleveland Clinic Taussig Cancer Institute, who commented on these and other study results presented at the press briefing earlier this afternoon. Saltzman noted aspirin’s side effects and said these results suggest that colorectal cancer prevention may be a secondary benefit for GLP-1s, beyond their primary use for managing diabetes and losing weight.

The ASCO news release about the study noted that while the relative risk reduction was fairly large, more than 2,000 people would need to be treated with a GLP-1 for one person to experience a lower risk of developing colorectal cancer. However, the ASCO news release said as many as 20 million Americans are taking a GLP-1. Applying that 1-in-2,000 ratio means roughly 10,000 people in the U.S. who are taking GLP-1s are gaining some colorectal cancer protection.

The evidence for a protective effect relative to aspirin was strongest for liraglutide, which is sold under the brand name Victoza, followed by dulaglutide, sold under the brand name Trulicity, and semaglutide. Tirzepatide, sold as Mounjaro for diabetes and Zepbound for weight loss, was also protective, but the statistics about its protective effects were less certain (the wide confidence interval included a hazard ratio of greater than 1.0).

The apparent superiority of GLP-1s to aspirin was even greater among the people who started with a higher risk of getting colorectal cancer because of family history or other factors. In the high-risk group, those taking a GLP-1 were 42% less likely to get colorectal cancer than those taking aspirin.

Age also had an effect, with the results suggesting more protection from GLP-1s than aspirin in those who started taking GLP-1s before they were 45. The results still pointed to protection in older people but with less statistical certainty.

The finding that GLP-1s might fend off colorectal cancer didn’t come out of the blue. Preclinical research has found that the drugs influence biological pathways implicated as causative of cancer and inflammation. Obesity increases the risk of colorectal cancer, but this study found that the GLP-1s reduced the risk of colorectal cancer regardless if the study participant had obesity or diabetes.

The study’s lead author, Colton Frisco Jones, M.D., a hematology/oncology fellow at the University of Texas San Antonio, billed it as the first real-world comparison between GLP-1s and aspirin for primary prevention of colorectal cancer. Jones and his colleagues used the TrinetX database to identify 140,828 people taking GLP-1s who could be matched demographically and otherwise to the same number of people taking aspirin.

The ASCO Gastrointestinal Cancer Symposium is scheduled to be held on Jan. 8-10 in San Francisco. It is common for ASCO and other medical groups to hold press briefings about attention-getting research findings in advance of the meetings and when the researchers will officially present their results.