In a new study of more than 1,200 Asian women, those who took aspirin at least a couple of times a week had a much lower risk of developing lung cancer -- whether or not they had ever smoked.
The findings, which link regularly taking aspirin to a risk reduction of 50 percent or more, do not prove that aspirin directly protects against lung cancer. There may be other explanations for the connection.
But the study backs up a number of previous ones linking regular aspirin use to lower risks of certain cancers, including colon, prostate and esophageal cancers.
Still, experts say it's too early to recommend widespread aspirin use for cutting cancer risk.
Even low-dose aspirin carries risks, like stomach irritation and ulcers.
"The question about whether aspirin use protects against lung cancer is still open to considerable debate at this point, and the published evidence to date is not conclusive," Dr. Wei-Yen Lim, who led the new study, said in an email.
Avoiding tobacco smoke remains the best way to protect yourself, said Lim, of the National University of Singapore.
Published in the journal Lung Cancer, the study included 398 Chinese women diagnosed with lung cancer and 814 cancer-free women.
Lim's team found that women who had used aspirin regularly -- at least twice a week for one month or longer -- were less likely to have lung cancer.
Among women who'd never smoked, the odds were 50 percent lower for aspirin users versus non-users. And among smokers, aspirin use was tied to a 62 percent lower risk of lung cancer.
The researchers were able to account for some other factors, like the women's age, education and fruit and vegetable intake. But there could still be other differences that would help explain why aspirin users had a lower lung cancer risk, according to Lim.
This type of study, the researcher said, is not designed to show whether taking aspirin cuts cancer risk. That takes a clinical trial, where people are randomly assigned to take aspirin or not.
And the findings do not give an idea of how much risk-reduction there might be.
There was a fairly large relative difference in cancer risk between aspirin users and non-users in the study. But the absolute reduction in any one person's risk, if there is one, might be small.
Other studies have linked regular aspirin use to lower risks of several types of cancer. Most recently, an analysis of past clinical trials found that people given daily low-dose aspirin were less likely to develop cancer after three years of use.
Aspirin appeared to prevent about three cases of cancer per 1,000 aspirin users per year.
There are also biological reasons that aspirin might offer protection: it blocks an enzyme called cyclooxygenase-2, or COX-2, which promotes inflammation and cell division and is found in high levels in tumors.
Dr. Andrew T. Chan of Harvard Medical School, who was not involved in the study, said that the evidence on aspirin and lung cancer has been "mixed."
"The number-one thing a person can do to minimize the risk of lung cancer is to not smoke," he said in an interview.
On the other hand, there is stronger evidence that aspirin may be protective against colon cancer, according to Chan, a gastroenterologist who researches colon cancer prevention.
"I don't think the evidence is definitive," Chan said. And it's too soon to recommend that all middle-aged and older adults take a daily aspirin.
But it may be reasonable for people to discuss the pros and cons of low-dose aspirin with their doctors, according to Chan.
"People are usually interested in more than preventing one particular cancer," he noted. "So it's important to view this in the context of a person's overall health."
That includes understanding the risks of aspirin. For many people, gastrointestinal side effects may be "minor," Chan said.
But some people can develop bleeding ulcers. Aspirin is also linked to an increased risk of hemorrhagic stroke -- bleeding in or around the brain.
Many middle-aged and older adults already take daily aspirin for their cardiovascular health.
The U.S. Preventive Services Task Force recommends that men age 45 to 79 take aspirin to prevent heart attacks, as long as their personal benefit is likely to outweigh the risk of bleeding. For women age 55 to 79, aspirin is recommended to prevent ischemic strokes (strokes caused by a blood clot), with the same caveat.
Lim said that if your doctor has recommended aspirin to you, stick with that advice.
"For people who are currently well," the researcher said, "we do not recommend taking aspirin to reduce their risk of lung cancer, as the effect of aspirin on lung cancer is still being evaluated."