A daily dose of adult-strength aspirin may modestly reduce cancer risk in populations with high rates of colorectal, prostate, and breast cancer if taken for at least five years.
The Women's Health Study trial recently reported that long-term use of low-dose aspirin (about 100mg every other day) does not reduce a woman's cancer risk, but it did not examine whether high doses of aspirin have an effect on cancer risk.
Eric Jacobs, Ph.D., of the American Cancer Society in Atlanta, and colleagues looked for associations between long-term daily aspirin use (at least 325mg/day) and cancer incidence in a group of nearly 70,000 men and 76,000 women. Aspirin use was determined by a questionnaire.
During the 12 year follow-up, nearly 18,000 men and women in the study were diagnosed with cancer. The researchers found that daily use of adult-strength aspirin for at least five years was associated with an approximately 15 percent relative reduction in overall cancer risk, though the decrease was not statistically significant in women. Additionally, aspirin use was associated with a 20 percent reduced risk of prostate cancer and a 30 percent reduced risk of colorectal cancer in men and women, compared to people who didn't take aspirin. There was no effect on risk in other cancers examined, lung cancer, bladder cancer, melanoma, leukemia, non-Hodgkins lymphoma, pancreatic cancer, and kidney cancer. Aspirin use for less than five years was not associated with decreased cancer risk.
"Our results do not have immediate clinical implications. Confirmation from randomized trials is necessary before a reduction in cancer risk could be considered a benefit of using adult-strength aspirin. Our results indicate that a randomized trial examining the effect of aspirin on cancer incidence would need to be both large and long term, probably lasting a minimum of 10 years. More evidence is needed before any such trial can be justified," the authors write.
In an accompanying editorial, Maria Elena Martinez, Ph.D., of the Arizona Cancer Center in Tucson, and E. Robert Greenberg, M.D., of the Fred Hutchinson Cancer Center in Seattle, write that, for the average person, the side effects of daily long-term aspirin use, such as intestinal bleeding or stroke, might outweigh the its benefits of cancer prevention. "However, if aspirin were shown to truly prevent a multitude of common cancers, there might be clinical situations in which daily adult-strength aspirin would be indicated," the authors write.