A large observational study has found that men who took aspirin regularly after their prostate cancer diagnosis were less likely to die from the disease, however aspirin did not affect the overall incidence of prostate cancer. The study was presented at the 2016 Genitourinary Cancers Symposium in San Francisco.

"It is premature to recommend aspirin for prevention of lethal prostate cancer, but men with prostate cancer who may already benefit from aspirin's cardiovascular effects could have one more reason to consider regular aspirin use," said lead study author Christopher Brian Allard, MD, Urologic Oncology Fellow at Brigham and Women's Hospital and Massachusetts General Hospital in Boston, Massachusetts. "When discussing potential benefits of aspirin with their doctors, in terms of both cardiovascular health and risk of prostate cancer death, men should also consider potential risks of regular aspirin use."

Many studies have looked at medications and supplements that help reduce the risk of death from prostate cancer among healthy men or prolong survival of men with prostate cancer. Prior studies on aspirin and prostate cancer prevention have reported conflicting findings. According to the authors, this is the first study to specifically focus on prevention of lethal cancer, clarifying the role aspirin may play in prevention of advanced disease. 

The researchers analyzed data from 22,071 men enrolled in the Physicians' Health Study. Over 27 years of follow-up, 3,193 men were diagnosed with prostate cancer. Of those, 403 men developed lethal prostate cancer, defined as metastatic disease or death from prostate cancer.

After adjusting for differences in age, race, body mass index, and smoking status, men without a diagnosis of prostate cancer who took aspirin regularly (more than three tablets a week) had a 24% lower risk of developing lethal prostate cancer. However, aspirin did not affect the likelihood of being diagnosed with total prostate cancer, high-grade prostate cancer, or locally advanced prostate cancer.

Among men with prostate cancer, regular aspirin use after diagnosis was associated with a 39% lower risk of dying from prostate cancer. In contrast, use of aspirin before diagnosis did not have a measurable benefit.

"We think that aspirin probably prevents progression of prostate cancer to metastases," said Dr. Allard. While the biological basis for this protective effect is unknown, preclinical research suggests aspirin may prevent the spread of cancer to the bone.

Dr. Allard and his research team will continue to explore the ways aspirin decreases risk of prostate cancer death. Meanwhile, more research is needed to determine which men in particular would benefit from regular aspirin and what the optimal dose of aspirin is.

The Physicians' Health Study began in 1982 to test the benefits and risks of aspirin and beta carotene in the primary prevention of cardiovascular disease and cancer. Thirty years and more than 400 published research reports later, the study continues. After the original randomized trial ended in 1995, researchers continued to follow study participants through annual questionnaires.

"This study suggests there may be yet one more benefit of aspirin, beyond those we've already seen in colorectal cancer and heart disease," said Sumanta Pal, MD, American Society of Clinical Oncology (ASCO) Spokesperson. "While taking aspirin does carry certain side effects that patients should discuss with their physician, it's intriguing that this low-cost medicine may lower the risk of death from prostate cancer."

This study received funding from the Prostate Cancer Foundation and the National Institutes of Health/National Cancer Institute.