What Works at 50 May Backfire at 70: New Aspirin-Cancer Study Challenges Conventional Wisdom

A daily aspirin that might help prevent cancer when started at 50 appears to offer no protection when begun at 70, and may even increase the risk of cancer death, according to a major study that followed nearly 20,000 older adults for almost a decade.

The research challenges the long-standing idea that aspirin’s cancer benefits apply at every age. While earlier studies in middle-aged adults found that aspirin could reduce cancer risk, particularly colorectal cancer, this new analysis shows those findings don’t translate to older adults. In fact, people who started taking 100 milligrams of aspirin daily after age 70 faced a 15% higher risk of dying from cancer compared to those taking a placebo.

The study, published in JAMA Oncology, tracked participants from the ASPREE trial and its extension for a median of 8.6 years. Aspirin neither lowered overall cancer rates nor prevented colorectal cancer in this age group. The findings challenge decades of medical thinking about aspirin as a one-size-fits-all cancer prevention tool and indicate that the body’s response to the medication changes with age.

How the Study Worked

The ASPREE trial enrolled 19,114 community-dwelling adults from Australia and the United States between 2010 and 2014. Australian participants were at least 70 years old, while U.S. participants from Black and Latino communities were at least 65. All were free of cardiovascular disease, dementia, and physical disabilities at the start.

Half took 100 milligrams of aspirin daily, while the other half took a placebo. Neither participants nor researchers knew who received what until June 2017, when the trial ended after a median of 4.7 years. Many participants then joined an extension study called ASPREE-XT, which tracked their health through 2024.

Researchers collected information about cancer diagnoses, stages, and deaths through medical records and participant reports. An expert panel reviewed all cases to confirm details. Over the full period, 3,448 participants developed cancer and 1,173 died from cancer. The median age at enrollment was about 75 years, and 56% were female.

Aspirin and Cancer Risk in Older Adults: No Protection, Higher Deaths

Aspirin offered no protection against cancer. Rates were virtually identical between groups across all cancer types and stages. But among those who developed cancer, people taking aspirin were more likely to die from their disease: 7.8 deaths per 1,000 person-years compared to 6.8 in the placebo group.

The pattern became clearer when researchers examined cancer by stage. Aspirin showed no effect on deaths from early-stage cancers (stages 1 through 3). But for stage 4 cancers that had spread throughout the body, death rates climbed higher in the aspirin group, with the difference emerging about four years into the study.

Colorectal Cancer and Aspirin: Challenging Decades of Research

One of the most anticipated findings involved colorectal cancer, the type most commonly linked to aspirin benefits in previous studies. The ASPREE study found no difference in colorectal cancer rates between aspirin and placebo users, and no difference in deaths from the disease.

This contradicts earlier research. The Women’s Health Study, which followed middle-aged women, reported a 42% drop in colorectal cancer among aspirin users 11 to 18 years after the trial ended. But those participants were younger, averaging age 55 when they started aspirin.

Other cancers showed mixed results. Prostate, breast, lung, and bladder cancers occurred at similar rates in both groups. Melanoma stood out as an exception: aspirin users had a 23% lower risk, which might be particularly relevant for the study’s largely Australian population where sun exposure and melanoma rates are high. The researchers caution that this melanoma finding could be a statistical fluke rather than a true protective effect.

What Happens After Stopping Aspirin?

After the trial ended, researchers kept tracking participants to see if effects from earlier aspirin use would linger. This analysis included 14,907 participants who hadn’t developed cancer during the trial.

During the extended observational follow-up (median 4.3 years post-trial), the groups started to converge. Those originally assigned to aspirin had slightly lower cancer rates, though the difference didn’t reach statistical certainty. More telling, the higher cancer death rate seen in the aspirin group during the trial disappeared. Death rates became essentially identical regardless of which pill participants had taken years earlier, suggesting aspirin’s effects on cancer in older adults don’t persist after stopping the medication.

Why Age Changes Everything for Aspirin and Cancer

Why would aspirin work differently in older adults? One likely explanation is how aging transforms the body’s biology.

As people age, their immune systems gradually weaken, a process scientists call immunosenescence. At the same time, older adults develop low-level chronic inflammation throughout their bodies. Both changes might interfere with how aspirin affects cancer cells and the body’s cancer surveillance systems.

Aspirin is thought to work against cancer partly by blocking certain inflammatory chemicals and preventing blood platelets from helping tumors spread. But in older adults with compromised immune systems, aspirin might inadvertently dampen the immune system’s ability to detect and destroy cancer cells. Some researchers speculate this could explain why aspirin appeared to increase advanced cancer and cancer deaths in this older population.

The cancers themselves also differ by age. Colorectal cancers in older adults are more likely to occur on the right side of the colon and more often have specific genetic features that might make them less responsive to aspirin. Gene mutations accumulate with age, potentially changing how tumors behave and respond to preventive treatments.

Supporting this age theory, other studies have found similar patterns. The Japanese Primary Prevention of Atherosclerosis with Aspirin for Diabetes trial found aspirin reduced cancer among those younger than 65 but not those 65 or older. Another study of more than 94,000 participants over 34 years found aspirin lowered colorectal cancer risk only among people who started using it before age 70.

What Older Adults Should Know About Taking Aspirin for Cancer Prevention

For older adults considering aspirin to prevent cancer, this study offers clear guidance: starting a daily aspirin regimen after age 70 doesn’t reduce cancer risk and might increase the chances of dying from cancer.

This doesn’t mean aspirin has no role in cancer prevention. Evidence still suggests benefits when started earlier in life, particularly for people at average risk in their 40s, 50s, or early 60s. But beginning aspirin at 70 or older for cancer prevention doesn’t appear to help.

These findings also don’t apply to people already taking aspirin for other reasons, such as preventing heart attacks or strokes after cardiovascular disease. Those individuals should talk with their doctors about whether to continue based on their specific situation. Researchers plan to keep following ASPREE participants longer, since cancer can take 10, 15, or even 20 years to develop.

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Medical Disclaimer: This article is for informational purposes only and is not intended as medical advice. Do not start or stop taking aspirin or any medication without consulting your healthcare provider. Aspirin may be prescribed for various medical conditions, and decisions about its use should be made in consultation with a qualified physician who knows your complete medical history.

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