Should you take an aspirin every day or two to lower your risk of cancer? Medical groups such as the American Cancer Society have so far recommended against the practice, but that might soon change as evidence stacks up in favor of taking aspirin for preventing colon cancer.
In a study published Monday, Brigham and Women’s Hospital researchers found that women who took a small dose of aspirin every other day for 10 years had a 20 percent lower risk of developing colon cancer over the next 16 years compared with those who took a placebo. About 1.1 percent of the aspirin takers developed colon cancer compared with 1.4 percent of those who took placebos, according to the findings published in the Annals of Internal Medicine.
The clinical trial, involving nearly 40,000 women involved in the Women’s Health Study, falls in line with results from other studies that “suggest aspirin is an effective way to prevent colorectal cancer,’’ said Dr. Andrew Chan, a gastroenterologist at Massachusetts General Hospital who was not involved in the research. “What’s not been clearly resolved is what is the optimal dose. Is a low-dose taken every other day just as effective [as a daily dose]? Does it lower the risk of side effects?’’
Side effects associated with regular aspirin use include stomach ulcers, gastrointestinal bleeding, and, in very rare cases, strokes caused by brain bleeds. The new study found that aspirin use raised a woman’s risk of developing an ulcer or having gastrointestinal bleeding by about 1 percent.
Whether the study’s low aspirin dose, 100 milligrams every other day, led to fewer side effects than a regular 325-milligram dose taken daily is tough to say.
“It’s difficult to compare studies since they were all conducted differently and didn’t always report milder side effects like ulcers,’’ said study leader Nancy Cook, a biostatistician at the Brigham. Most, like the Women’s Health Study, were designed to see whether daily aspirin use prevents heart disease and only coincidentally found lower cancer rates.
The latest study didn’t find that aspirin lowered the risk of breast or lung cancers; other research suggests there may be some protective effect, but the evidence is weaker for these cancers than for colon cancer. And scientists still aren’t exactly sure how aspirin’s ability to reduce inflammation might thwart the growth of cancer cells.
Chan said he’d also like to see further research to determine whether taking a higher dose of aspirin provides added protection from colon cancer. The research done so far indicates that a daily dose might offer this protection sooner than taking aspirin every other day; the Women’s Health Study didn’t find any decrease in colon cancer rates until about 16 years, far later than other studies that used daily doses.
Due to all these unknowns, the American Cancer Society recommends against taking aspirin to prevent cancer and “has no immediate plans to consider amending their advice,’’ said Eric Jacobs, the organization’s strategic director of pharmacoepidemiology.
It is waiting for an expert group of primary care physicians — called the US Preventive Services Task Force — to review the latest research and issue an updated recommendation, which the group plans to do within the next year.
“If they were to start recommending aspirin use for cancer prevention, that’s something we would take into account,’’ Jacobs said. “But it’s still important to emphasize the importance of colon cancer screening since colonoscopies can detect and remove polyps before they turn into cancer.’’
In 2007, the Task Force recommended against using aspirin to prevent colon cancer after concluding that the risks outweighed the benefits. (It does, however, recommend daily aspirin use to prevent heart attacks and strokes in certain people who are at increased risk.)
With the latest evidence pointing to aspirin’s potential to reduce colon cancer, Cook said she thinks some patients at increased risk may want to talk to their doctors about whether they could benefit overall from taking a low-dose pill every day or two.
“They need to balance overall risks and benefits,’’ she said, “and it looks like the benefits may be greater for those with a family history of colon cancer or who have already had colon polyps.’’
A study published earlier this year found that those who carried a gene for a rare hereditary form of colon cancer were able to lower their rate of colon cancer by nearly 40 percent by taking 600 milligrams of aspirin daily for five years.
Other researchers have identified new biomarkers that appear to predict which patients might get bigger colon cancer prevention benefits from aspirin use.
“We’re not at the point where we can screen for these markers, but that’s where researchers are heading,’’ Cook said.