Can Aspirin Prevent Cancer?

Jared Hirschfield, Tracy Rupp, PharmD, MPH, RD, Laura Gottschalk, PhD, Cancer Prevention and Treatment Fund

Doctors have prescribed aspirin to prevent heart attacks and strokes for many years. In the past five years, researchers have begun to study whether daily low-dose aspirin use can also prevent cancer. In response to early evidence that aspirin may protect against colon cancer, in 2016 experts began recommending an aspirin a day to prevent colon cancer.[1] More recent and more reliable studies, however, have not shown a lower risk of cancer among people who take daily aspirin. It’s clear that more research is needed to confidently determine whether such an effect exists.

Recommending Aspirin for Cancer Prevention

The U.S. Preventative Service Task Force (USPSTF), an independent group of medical experts, currently recommends that people between the ages of 50 and 59 take 81 mg of aspirin daily (the typical dosage of “baby” or low-dose aspirin) to prevent colon cancer.[1] Daily aspirin is not safe for everyone in this age group, however. For example, if you have an increased risk of bleeding from other medications or a history of stomach or intestinal ulcers, kidney disease, or severe liver disease, the risks of taking aspirin likely outweigh any potential benefits.

The preliminary finding that aspirin might prevent death from cancer originated in part from a 2016 study published in the Journal of the American Medical Association (JAMA).[3] Using data from almost 48,000 men and more than 88,000 women who were enrolled in two long-term observational studies (The Nurses’ Health Study and the Health Professionals Follow-up Study), the researchers found that people who took aspirin regularly had a slightly lower risk for overall cancer and a 19% lower risk for colon cancer.

More recent studies, based on randomized, double-blind, placebo-controlled clinical trials, did not support that finding. The first trial, which was part of the larger ASCEND (A Study of Cardiovascular Events in Diabetes) study, enrolled more than 15,000 patients with diabetes and found no evidence that aspirin prevents colon cancer or any other cancers.[4] The second trial, part of the larger ASPREE (Aspirin in Reducing Events in the Elderly) study, enrolled more than 19,000 patients above the age of 70 and found a very tiny increased risk of cancer in the daily aspirin group as compared to placebo.[5] While the very small increased risk does not seem meaningful, it is clear that neither of these studies found evidence that aspirin provides a protective factor against cancer for these groups of patients (patients with diabetes and patients who are older than 70).

These new results are important because both the ASCEND and ASPREE studies were randomized controlled trials (RCTs), comparing people who were randomly assigned to take aspirin to people who were randomly assigned to take a placebo that looked like aspirin. In contrast, observational studies, such as the JAMA study published in 2016, analyze the difference between participants who choose themselves whether or not to take aspirin. The people who choose to take aspirin may have better health habits or differ from those who don’t in other ways. That is why, as a general rule, the results of large randomized controlled trials are much more accurate than observational studies.  

Given these different results for different types of studies of somewhat different groups of patients, the impact of daily aspirin on cancer is still unclear. Early studies seemed to suggest a preventive effect, but newer, more reliable trials have not shown any evidence that daily aspirin use reduces your risk of developing cancer. More research is needed on this topic to conclusively determine whether the benefits of daily aspirin outweigh the risks for adults aged 50 to 59. It is unlikely that daily aspirin has benefits for people over 70.

All articles are reviewed and approved by Dr. Diana Zuckerman and other senior staff.

Footnotes:

  1. USPSTF. Final Update Summary: Aspirin Use to Prevent Cardiovascular Disease and Colorectal Cancer: Preventive Medication. April 2016. Available online: https://www.uspreventiveservicestaskforce.org/Page/Document/UpdateSummaryFinal/aspirin-to-prevent-cardiovascular-disease-and-cancer
  2. American Association for Cancer Research News Release. Regular Aspirin Use in Associated with Lower Cancer Mortality. April 3, 2017. Available online: http://www.aacr.org/Newsroom/Pages/News-Release-Detail.aspx?ItemID=1036#.Wib80kqnGM9
  3. Cao Y, et al. Population-wide Impact of Long-term Use of Aspirin and the Risk for Cancer. JAMA Oncol. Published online March 03, 2016. DOI: 10.1001/jamaoncol.2015.6396
  4. The Ascend Study Collaborative Group. “Effects of Aspirin for Primary Prevention in Persons with Diabetes Mellitus.” The New England Journal of Medicine (August 2018). https://www.nejm.org/doi/full/10.1056/NEJMoa1804988.
  5. McNeil, J.J. et al. “Effect of Aspirin on All-Cause Mortality in the Healthy Elderly.” The New England Journal of Medicine (October 2018). https://www.nejm.org/doi/full/10.1056/NEJMoa1803955
  6. U.S. National Library of Medicine. MedlinePlus: Drugs, Supplements, and Herbal Information. Accessed December 2017. https://medlineplus.gov/druginfo/herb_All.html.