Can Aspirin Avert Lethal Prostate Cancer? Long-term Study Suggests a Possible Role

Christopher Brian Allard, MD

Aspirin’s benefits may now extend to reducing the risk of deadly prostate cancer, according to the results of an observational study which found that previously undiagnosed men who took regular aspirin had a 24% lower risk of developing a lethal form of the disease. Moreover, among men already diagnosed, those who took aspirin lowered their risk of dying from prostate cancer by 39%.

However, regular aspirin use before diagnosis did not confer a measurable benefit for the prevention of overall, high-grade, or locally advanced prostate cancer, reported Christopher Brian Allard, MD, during a presscast held in advance of the 2016 Genitourinary Cancers Symposium.

“Our study demonstrates that regular aspirin intake may inhibit lethal prostate cancer, probably by preventing cancer progression,” said Allard, the study’s lead author and a urologic oncology fellow at Brigham and Women’s Hospital and Massachusetts General Hospital. “Men with prostate cancer who took aspirin regularly after diagnosis had a significantly reduced risk of death.”

For their study, researchers followed 22,071 men who were enrolled in the Physicians’ Health Study between 1982 and 2009. Participants’ aspirin use and prostate cancer status were reviewed annually via questionnaires and review of hospital records. The primary focus of the research was whether there was a relationship between regular aspirin use (defined as more than 3 tablets per week) and lethal prostate cancer (defined as metastatic disease or death from prostate cancer). The study marked the first to specifically examine this relationship, its authors noted.

After 27 years of follow-up, 3193 men developed prostate cancer, of which 403 cases were lethal. After adjusting for differences in age, race, body mass index, and smoking status, men without prostate cancer who took aspirin regularly had a 24% lower risk of developing the disease (HR, 0.76; 95% CI, 0.62-0.93).

“When we looked at the subset of men who were already diagnosed with prostate cancer,” Allard continued, “we found that regular aspirin intake decreased the risk of prostate cancer death by almost 40%,” (HR, 0.61; 95%CI, 0.47-0.78).

Allard theorized that aspirin’s benefit may stem from its role in inhibiting platelets. He explained that because platelets probably shield circulating cancer cells from immune recognition, “by depleting those platelets, you’re allowing the immune system to recognize the cancer.” He added that this hypothesis is supported by some animal studies: “That would explain why there is no effect on the local cancer, but it is preventing deposition of metastases into metastatic environments.”

The main limitation of the study, noted Allard, is the variability in dose and frequency of aspirin use over the nearly 3 decades of participant follow-up. When the Physicians’ Health Study was launched in 1982 as a randomized trial, participants took aspirin every other day at a dose of 325 mg, but that trial was stopped after 5 years when aspirin’s cardiovascular benefit was clearly established; thereafter, men were followed for another 22 years, and Allard explained that although they provided detailed reports of frequency of aspirin use, “it wasn’t always clear what dose they were taking,” though 81 mg did emerge as a popular dose.

Allard said that he and colleagues will continue to explore how aspirin may decrease the risk of prostate cancer mortality, adding that “more work is needed to identify particular subsets of men most likely to benefit from aspirin use and to determine the optimal aspirin dose.”

“It is premature to recommend aspirin use 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 Allard, adding that men considering aspirin use should consult their physician to discuss benefits and risks.

Presscast moderator and ASCO expert Sumanta Pal, MD, noted that whereas “we often think of prostate cancer as being a rather slow-growing or indolent disease, it’s really important to keep in mind that over 25,000 men die of prostate cancer each year.”

“This study suggests that there may be yet one more benefit of aspirin, beyond those we’ve already seen in colorectal cancer and heart disease, Pal continued. “While this work is provocative, it is important to keep in mind that the findings are from an observational study … these studies are certainly thought-provoking but are perhaps best followed by formal clinical trials where we compare use of aspirin either to no treatment or perhaps a placebo.”

Allard CB, Downer MK, Preston MA, et al. Regular aspirin intake and the risk of lethal prostate cancer in the physicians’ health study. Presented at: 2016 Genitourinary Cancers Symposium; January 7-9, 2016; San Francisco, CA. Abstract 306.

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