Millions of people take low-dose aspirin to help prevent heart attacks, but accumulating evidence suggests that the drug’s greatest benefit may actually be in reducing the risk of cancer, especially colorectal cancer.
Unfortunately, aspirin has well-known risks, notably bleeding in the stomach and brain, so doctors are rightly hesitant to recommend its routine use. Now a comprehensive review in the Annals of Oncology, using data from hundreds of studies, has made the strongest case yet for aspirin as a cancer preventive by putting the benefits and risks in perspective.
The main finding: Taking aspirin daily for 10 years after age 50 may cut the risk of colorectal, stomach, and esophageal cancers by about one-third, and reduce death rates from them even more. There were small— and less clearcut—reductions in prostate, breast, and lung cancers. At the same time, there was an 18 percent drop in heart attacks and a small drop in deaths from them.
The benefits accrued when people took aspirin daily for at least three years between the ages of 50 and 65. They increased with 10 years of aspirin use and seemed to persist for at least five years after aspirin was stopped. Most of the studies used the low dose of aspirin commonly taken for heart health.
The risk of major gastrointestinal bleeding was found to increase by about one-third (occurring in about 2 percent of aspirin users over a 10-year period), but this was seldom life-threatening, especially in people under 70. The most serious consequence, though relatively rare, was a higher risk of death from hemorrhagic stroke (the less-common type of stroke, caused by bleeding in the brain).
Here’s a way to simplify the reams of numbers in the analysis: If 1,000 people took daily aspirin for 10 years starting at age 60, it would prevent about 16 deaths from cancer and one death from a heart attack, but cause two extra deaths from bleeding (mostly from hemorrhagic strokes). In total, there would be about 8 percent fewer cases of cancer, heart attacks, and ischemic strokes and 4 percent fewer deaths over a 20-year period.
Hardly the last word
Those findings sound more definitive than they are. The studies in the analysis were not designed to look at cancer, and that can complicate the interpretation of the results. Randomized trials focusing on aspirin’s effect on cancer are underway.
Moreover, this new review leaves some key questions unanswered. What’s the optimal dose of aspirin to prevent cancer and how long should it be taken? The researchers suggested that low-dose aspirin is as effective as higher doses and less risky, that 10 years may be adequate (thanks in part to a “carry-over effect”), and that it would be prudent for most people to stop at age 70 because the risk of serious bleeding roughly doubles with each passing decade.
How can we predict who is most likely to benefit and who is likely to have adverse effects? Ongoing research, it’s hoped, will provide answers. Notably, recent studies suggest that certain genetic markers may identify those people in whom aspirin would reduce the risk of colorectal cancer.
Bottom line: It’s still premature to recommend routine use of low-dose aspirin to prevent cancer. But you should discuss it with your doctor, especially if you are at high risk for developing colorectal cancer. Certain people, such as those with ulcers, bleeding disorders, or a history of gastrointestinal bleeding, shouldn’t take aspirin.