Long-term Aspirin Tied to Small Drop in Overall Cancer Risk

Veronica Hackethal, MD

March 08, 2016

Regular, long-term use of low-dose aspirin is linked to a small decrease in overall cancer risk, with much of the reduction due to decreased gastrointestinal (GI) cancers, particularly colorectal cancer (CRC), new research involving more than 135,000 adults indicates.

"It's a very exciting time for the field of cancer prevention. There does seem to be an effective and low-cost option for cancer prevention that could have widespread implications for many individuals," commented lead study author Andrew T. Chan, MD, MPH, of the Massachusetts General Hospital, Boston, Massachusetts.

"At the same time, I would caution people from believing aspirin is a cure-all and should be used without concern for other potentially effective ways of preventing cancer," he stressed.

Dr Chan told Medscape Medical News that aspirin is a complement to other cancer-prevention strategies.

The new data, which come from two large cohorts and more than 30 years of follow-up, were published online March 3 in JAMA Oncology.

Dr Chan and colleagues reported that, compared to nonregular aspirin users (aspirin use less than two times per week or not at all), regular users had 3% lower risk for overall cancer (relative risk [RR], 0.97; 95% confidence interval [CI], 0.94 - 0.99), with much of the reduction due a 15% lower risk for GI cancers (RR, 0.85; 95% CI, 0.80 - 0.91) and a 19% lower risk for CRC (RR, 0.81; 95% CI, 0.75 - 0.88).

The new data add to a growing literature on the positive effects of aspirin on cancer.

For example, recent data presented at the European Cancer Congress (ECC) 2015 suggested that taking low-dose aspirin after diagnosis nearly doubled 5-year survival rates among a range of GI cancers, as reported by Medscape Medical News.

A 2014 review by UK investigators found that the health benefits of aspirin outweigh its harms (such as GI bleeding and hemorrhagic stroke). The review confirmed what one expert has called an "emerging consensus by some of the best minds in the field" in support of a role for aspirin in cancer prevention, but fell short of making a clear recommendation, as reported by Medscape Medical News.

In 2015, the US Preventive Services Task Force recommended long-term (at least 10 years) daily low-dose aspirin for the prevention of cardiovascular disease (CVD) and CRC in adults aged 50 to 69 years who have increased CVD risk.

"Our study adds to the data to support the rationale for these recommendations," Dr Chan said.

In a linked editorial, Eduardo Vilar, MD, PhD, Karen Colbert Maresso, MPH, and Ernest T. Hawk, MD, MPH, of the University of Texas MD Anderson Cancer Center, Houston, noted numerous strengths of the study and pointed out that the results are "generally consistent" with past studies.

However, they lamented the lack of an assessment of the potential harms of aspirin.

The jury is still out regarding aspirin as a cancer chemopreventative agent, suggests another expert.

"The American Cancer Society [ACS] recognizes the evidence that long-term, regular aspirin use has both harms and benefits, including reduced risk of CRC, but does not currently have recommendations for or against aspirin use," Eric Jacobs, PhD, strategic director of pharmacoepidemiology at the ACS, told Medscape Medical News in an email.

Study Details

In the study, researchers drew on data from two large, prospective, cohort studies: the Nurses' Health Study (1980-2010; 88,084 women) and the Health Professionals Follow-up Study (1986-2012; 47,881 men).

Participants self-reported their aspirin use and cancer diagnoses every 2 years. Researchers identified incident cancer cases using the National Death Index and obtained data on cancer type, stage, and histology from medical records.

During 32 years of follow-up, the study identified 20,414 cancer cases among women and 7571 cancer cases among men.

Using 2015 data, the above-mentioned 15% risk reduction for GI cancers translates into 29,800 GI cancers prevented each year with regular aspirin use, or 25% of cancer-related deaths averted, the authors point out.

Results were similar in women and men and did not change when 11 factors related to cancer were included in the analysis. These factors included age, BMI, family history, comorbidities, reproductive factors, smoking, and history of cancer screening.

Further analyses showed that regular aspirin use could prevent 17% of CRC in people older than 50 years who do not receive colonoscopy screening, and 8.5% of CRC in those who do receive screening.

The effect of regular aspirin use on GI cancers appeared to be dose dependent. To reap the benefits, the minimum duration of regular use appeared to be 6 years.

Regular aspirin use was not linked to risk for breast, advanced prostate, or lung cancer.

The study did not look at adverse side effects, such as GI bleeding and hemorrhagic stroke, and future studies should look at the balance of risks vs benefits of long-term aspirin use, according to Dr Chan.

"We're hopeful that this work will provoke a discussion between individuals and their physicians about the potential uses of aspirin for prevention of cancer," he concluded. "It still requires a careful consideration of the individual risks and benefits, in particular, the risk of bleeding."

In their editorial, the trio of MD Anderson experts say that they would like to have seen an evaluation of the "full range" of aspirin's benefits beyond cancer prevention, as well as its long- term effects on cancer-specific and all-cause mortality.

"To reflect accurately the often complex, real-world clinical scenarios in which physicians and patients contemplate the use of aspirin, any truly informative analysis of its use must weigh its cumulative benefits against its cumulative risks," they write.

Nevertheless, they editorialists conclude: "For now, learning that aspirin's preventive effects on GI tract cancer seem to extend even to those individuals who undergo CRC screening provides further support for aspirin's possible future use as a cancer preventive agent."

The ACS's Dr Jacobs said that the decision whether to take aspirin should be made in conversation with a healthcare provider who can assess an individual's CVD risk and discuss the pros and cons of regular aspirin use, he advised.

"Aspirin use is not a substitute for getting tested for CRC," he stressed. "All Americans 50 or older should talk to their healthcare provider about getting tested for CRC so that colorectal polyps can be detected and removed before they get a chance to develop into cancer."

Dr Chan reports consulting for Bayer Healthcare, Pfizer, Inc, and Pozen, Inc. The other authors and editorialists have disclosed no relevant financial relationships.

JAMA Oncol. Published online March 3, 2016. Full text, Editorial

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