The results of a recent clinical trial indicate that, for older adults with advanced cancer, initiating aspirin therapy may increase their risk of disease progression and early death. Notably, the vast majority of the study participants did not previously take aspirin before age 70.

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The study, conducted by Harvard Medical School researchers based at Massachusetts General Hospital and colleagues at the Berman Center for Clinical Outcomes and Research in Minnesota and Monash University in Australia, is published in the Journal of the National Cancer Institute.

“Deaths were particularly high among those on aspirin who were diagnosed with advanced solid cancers, suggesting a possible adverse effect of aspirin on the growth of cancers once they have already developed in older adults,” said senior study author Andrew Chan, professor of medicine at HMS.

The findings suggest the possibility that aspirin might act differently, at the cellular or molecular level, in older people, and further studies are needed to better understand the underlying mechanisms, said Chan, who is chief of the Mass General Clinical and Translational Epidemiology Unit and director of epidemiology at the Mass General Cancer Center.

Previous clinical trials have revealed compelling evidence that aspirin may reduce the risk of developing cancer, especially colorectal cancer predominantly in middle-aged adults. Information is lacking for older adults, however.

To provide insights, investigators designed and initiated the ASPirin in Reducing Events in the Elderly (ASPREE) trial, the first randomized double-blind placebo-controlled trial of daily low-dose aspirin (100 mg) in otherwise healthy older adults.

The study included 19,114 Australian and U.S. adults aged 70 or older, or aged 65 or older for U.S. Black and Hispanic participants, without cardiovascular disease, dementia or physical disability at the start of the study. Participants were randomized to receive aspirin or placebo and followed for a median of 4.7 years.

Surprising concern

In October 2018, the investigators published a surprising and concerning report showing an association between aspirin use and an elevated risk of death, primarily due to cancer. The current report now provides a more comprehensive analysis of the cancer-related effects of aspirin in the ASPREE participants.

“We conducted this study as a more detailed examination of the effect of aspirin on the development of cancer as well as death from cancer,” Chan said.

Chan and his colleagues reported that 981 participants who were taking aspirin and 952 who were taking placebo developed cancer.

Aspirin was associated with a 19 percent higher risk of being diagnosed with cancer that had spread or metastasized and a 22 percent higher risk of being diagnosed with stage 4, or advanced cancer.

Also, among participants who were diagnosed with advanced cancer, those taking aspirin had a higher risk of dying during follow-up than those taking placebo.

There was no statistically significant difference between the groups for developing cancer overall or for developing specific types of cancer.

“Although these results suggest that we should be cautious about starting aspirin therapy in otherwise healthy older adults, this does not mean that individuals who are already taking aspirin—particularly if they began taking it at a younger age—should stop their aspirin regimen,” said Chan.

Adapted from a Mass General news release.

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