So says a new review of studies published today. Still, many doctors say more must be known about the reasons for the possible benefit before their advice to their patients will change.
Researchers found that after five years, cancer death rates were 21 percent lower in patients assigned to take an aspirin a day -- a reduction in cancer risk that persisted for 20 years -- according to pooled data on a total of 25,570 individuals participating in eight randomized studies.
The meta-analysis, led by Peter M. Rothwell of John Radcliffe Hospital in Oxford, England, was published online in the journal The Lancet.
The researchers called the results "the first reliable evidence that aspirin prevents non-colorectal cancer in humans" -- a possibility to which earlier studies had pointed -- though the preventive effect was evident mainly in deaths from gastrointestinal cancers.
The researchers also said the findings may alter the way doctors view the benefits of daily aspirin in patients in light of the bleeding risk -- albeit a relatively small one -- associated with taking the drug.
"Our analyses show that taking aspirin daily for five to 10 years would reduce all-cause mortality (including any fatal bleeds) during that time by about 10 percent," the researchers wrote.
Mary Beth Terry, an associate professor at the Columbia Mailman School of Public Health in New York, said the findings are consistent with previous research that showed that aspirin prevents colorectal cancer.
"This builds on a very large body of evidence from observational studies suggesting that aspirin can reduce cancer risk of many different tumor sites, but because it analyzes individual data from randomized clinical trials it is very compelling," she said.
Rothwell and colleagues also cautioned, however, that the findings by themselves do not prove that aspirin prevents cancer or even cancer death. They said additional studies would be needed to determine what effect, if any, daily aspirin has on cancer incidence -- as well as the reason for this apparent effect.
The American Cancer Society agreed that it would be premature at this point to put everyone on daily aspirin.
"Even low-dose aspirin can substantially increase the risk of serious gastrointestinal bleeding," warned Eric Jacobs, a cancer society official, in a statement. "It will take time for expert guidelines committees to carefully consider these new results together with the existing evidence and consider for whom the benefits of aspirin use are likely to outweigh the risks."
Still, Jacobs called the study "a major contribution and provides important new evidence from randomized trials in humans that long-term daily aspirin use may lower mortality from certain cancers in addition to colorectal cancer."
Meanwhile, several physicians contacted by MedPage Today and ABC News said daily aspirin could be considered for at least some patients as a preventative measure for cancer.
Dr. Stefan Gluck, associate chief of hematology and oncology at the University of Miami, said in an e-mail that he had already been recommending daily aspirin to patients. He said the meta-analysis findings "only confirm what has been known for a while -- the nature of the study just makes the statement stronger."
Dr. Randy Wexler, a family medicine specialist at Ohio State University, said a general recommendation would not be warranted yet, "but in patients who do have risk factors, such as family history, this would be something to discuss and consider."
On the other hand, Dr. Clifford Hudis, chief of breast medicine at Memorial Sloan-Kettering Cancer Center in New York City, said the studies included in the meta-analysis weren't designed to address prevention of cancer death, and hence the findings need confirmation.
"What is badly needed is a prospective, disease-specific study that shows with placebo-control that either incidence, recurrence or death are significantly reduced," Hudis said. The studies in the review, he pointed out, were designed primarily to look at aspirin's potential in preventing heart problems, not cancer. "This clearly deserves a prospective study with cancer as the endpoint."
For now, said Dr. Alan Arslan, assistant professor of OB/GYN and Environmental Medicine at New York University, patients should not try to self-medicate in the hopes of lowering their risk of dying from cancer.
"The take-home message for patients is that if someone is taking low-dose or regular aspirin it may put them at a reduced risk of death from cancer," Arslan said. "However, if someone is not already taking aspirin they should talk with their physician before starting."