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Can aspirin fight cancer?

The medicine-cabinet staple seems to be a powerful weapon, though it’s not without risks.

Research has shown that aspirin’s ability to reduce the clotting of blood could play a role in its cancer-fighting abilities.

Lane Turner/Globe Staff/File

Research has shown that aspirin’s ability to reduce the clotting of blood could play a role in its cancer-fighting abilities.

Aspirin, a medicine cabinet staple for fighting heart attacks and headaches, is also a powerful weapon against cancer, a growing body of research shows.

“As mundane as it is, it’s really an incredible drug,” said Dr. John Baron, a professor of medicine at the University of North Carolina at Chapel Hill School of Medicine, who studies aspirin and cancer prevention. “My general opinion is that aspirin is probably good for a large majority of the adult population.”

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The groups most likely to benefit from aspirin’s anti-cancer powers, research suggests, are those at extra risk for colon cancer, and people between ages 50 and 75, said Dr. Andrew Chan, a gastroenterologist at Massachusetts General Hospital. Those older than 75 are at higher risk for aspirin’s side effects, and people younger than 50 stand to benefit less from its cancer-fighting effects, he said.

But for that middle age group, whether aspirin’s benefits outweigh its risks is still an open question. Aspirin can cause stomach upset and, rarely, life-threatening bleeding in the intestines or brain.

“It is a real drug and there are real risks,” Baron said.

When researchers first started noticing that aspirin seemed to ward off colon cancer in those who were taking aspirin for its heart benefit, they thought it was a fluke. But evidence has been accumulating that aspirin helps cut the risk of other forms of cancer, too, including stomach, pancreatic, and maybe even lung and breast cancer – by as much as 25 percent.

In a paper published earlier this month in the Journal of the National Cancer Institute, researchers looking at results from 12 different studies found that women who took a daily aspirin were at 20 percent lower risk for developing ovarian cancer than the general population.

In December, another paper in the same journal showed that people with a common version of one gene cut their colorectal cancer risk in half by taking a baby aspirin a day.

“It’s pretty clear now that aspirin is an effective chemotherapeutic agent,” said Chan, who led that study.

He now prescribes aspirin to many of his colon cancer patients to prevent recurrence. One of those patients, L. Stewart Keefe, 62, of Rochester, N.H., said she’s taken aspirin since her second bout with colon cancer a half-dozen years ago. She’s never had a problem with her daily regimen and is hopeful that the drug will help her avoid the fate of her mother, who died of colon cancer at age 26, and grandfather, who was killed by the disease in his early 50s.

“If it helps, great,” she said. “If it doesn’t, what have I lost?”

But if Keefe did have side effects, like a daily stomach ache, would it be worthwhile for her to take the aspirin? Would a daily aspirin regimen still be worthwhile for a person who doesn’t have her same elevated risk of cancer? What about for someone who has a higher risk of suffering from aspirin’s adverse effects?

Those are the kinds of questions scientists still can’t answer.

While studies find consistent benefits for aspirin, they’ve not been good at measuring the risks of an aspirin regimen, said Janusz Jankowski, a gastroenterologist and cancer prevention specialist at the Plymouth University Peninsula Schools of Medicine and Dentistry in the UK.

Many of the research trials have excluded the 20-30 percent of people at highest risk for side effects from aspirin – so it’s not surprising that the trials found that benefits outweigh risks, he said. Giving aspirin to a broader group of subjects will certainly lead to more complications, he said.

Further complicating the picture is that the cancer-reduction payoff will generally not be apparent until people are in their 70s and 80s. But people who begin taking aspirin too early could get far more ill effects than benefit.

At some point, researchers may know enough about aspirin to say with confidence who will benefit from taking it and who will be at most risk for dangerous side effects, Jankowski said.

Researchers also still need to learn how much aspirin people should take, and for how long. An 81 mg so-called baby aspirin, which is the recommended dosage to prevent heart attacks, seems to help fight cancer, Chang said. Higher doses may help more, though – but they come with a higher risk of side effects.

It’s also unknown how long someone should take aspirin in order to reduce their odds of getting cancer. It looks like five years of daily aspirin use is enough to reduce your cancer risks, according to Asad Umar, chief of the Gastrointestinal & Other Cancers Research Group in the Division of Cancer Prevention at the National Cancer Institute. But it’s possible that future research will show 7 or 10 years to be better, he said.

Another question that has not yet been answered is a fundamental one: Why does aspirin work in fighting cancer?

“How come this one drug, even at such a low dose prevents all kinds of cancer, when you need a very different treatment for ovarian cancer, colon cancer, breast cancer?” Umar asked.

Some expect that inflammation plays an underlying role in all these diseases, and that aspirin helps reduce inflammation – but this has yet to be confirmed.

Other research has shown that aspirin’s ability to reduce the clotting of blood could play a role in its cancer-fighting abilities.

Why is it so hard to pin down the answers to the many open questions about aspirin? In part, because it’s hard to study something that may have an effect decades later, said Chan, of Mass. General. Aspirin is also a generic medication, so there’s no large drug company pushing research, though Chan said he has done some consulting work for Bayer.

And because aspirin is so readily available in the United States, it’s tough to compare one group of people who take aspirin with another who doesn’t, said Umar of the National Cancer Institute.

There are now several large studies of aspirin underway in the US, UK, and Australia that should begin to answer some of these questions, Umar said.

Long-term, aspirin’s real benefit may come as inspiration for another drug, Jankowski said.

If aspirin helps about one in four people avoid cancer, why doesn’t it help the other three? Starting with that question, researchers are now trying to understand aspirin’s effects well enough to design a drug that extends the same benefits to more people, ideally with fewer risks, he said.

The bottom line, Jankowski said, is that while aspirin is effective at lowering cancer risk, there are safer ways to accomplish the same goal.

“If you want to cut your cancer rate by 50 percent, I can tell you what to do,” he said: Stop smoking, drink only in moderation, eat healthy foods, and avoid obesity. “We need to get the patients as healthy as we can without medications,” Jankowski said.

And for anyone who thinks they can compensate for an unhealthy habit by taking aspirin, Jankowski has some bad news:

“A tablet isn’t going to offset any of your natural lifestyle habits.”

Karen Weintraub can be reached at Karen@KarenWeintraub.com. Follow her on Twitter @kweintraub.
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