Women who recently and regularly take a daily low-dose aspirin may lower their risk of developing ovarian cancer, new research suggests.
The study highlights two important caveats. Daily use of standard-dose aspirin (325 milligrams) does not reduce the risk of ovarian cancer, and heavy use of nonaspirin nonsteroidal anti-inflammatories (NSAIDs), such as ibuprofen and naproxen, may increase the risk, suggests the study, published Thursday in the medical journal JAMA Oncology.
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Another potential limitation: The result was found only in women who had been using low-dose aspirin for less than a year.
Aspirin is believed to lower the risk of ovarian cancer -- the fifth most common cause of cancer-related death among American women -- by reducing inflammation, according to the authors.
The new analysis included data on 205,498 women who were part of the Nurses' Health Study and Nurses' Health Study II, two long-term studies that use questionnaires to track disease and health behavior in women.
Of those women, 1,054 developed ovarian cancer. The research team examined how these women used aspirin, non-aspirin NSAIDs and acetaminophen and compared their behavior with that of other participants.
Analysis showed that women who had been using low-dose aspirin for less than a year had a 23% lower risk of ovarian cancer than women who did not use aspirin at all. However, women who used low-dose aspirin for five years or longer and those who used standard-dose aspirin (325 milligrams) did not show improved odds against developing ovarian cancer, the study indicated.
By contrast, use of non-aspirin NSAIDs for less than a year was associated with a 19% increased risk of ovarian cancer, the researchers from the Harvard T.H. Chan School of Public Health found.
NSAIDs taken in quantities of at least 10 tablets per week for multiple years increased the risk of ovarian cancer by 34%. However, when NSAIDs were used less than two days a week for five years or longer, they were not linked to an increased risk of ovarian cancer.
Older women who take low-dose aspirin to reduce their risk of heart disease are not likely to increase their risk of ovarian cancer, the researchers concluded.
Other scientists believe further research is needed to verify the results.
Stephen Evans, a professor of pharmacoepidemiology at the London School of Hygiene & Tropical Medicine, told Science Media Centre the new analysis is "good, but the limitations in the data mean that the findings should be treated with caution."
"The results are slightly puzzling in relation to aspirin, with low doses showing a decreased risk and higher doses showing an increased risk," said Evans, who did not participate in the research. "This could be an indication that unmeasured factors are an explanation for the findings."
"Other pain-relieving drugs (NSAIDs) and aspirin at higher doses do not have this reassurance for long-term use," he said. "However, the risk for any particular individual, even if these findings are correct, is not high, and they may not be correct."
Eric J. Jacobs, a cancer epidemiologist and strategic director of pharmacoepidemiology at the American Cancer Society, said, "At best, the overall evidence suggests that aspirin only slightly lowers risk of ovarian cancer.
"There is still too little evidence to conclude that aspirin use helps lower risk of liver or ovarian cancer, and people should not take aspirin in the hopes of preventing these cancers," added Jacobs, who was not involved in the research.
The study authors also said that more research is needed to understand how "heavy use of aspirin, nonaspirin NSAIDs, and acetaminophen may contribute to the development of ovarian cancer."