Aspirin may cut bowel cancer risk – especially for those with ‘additional risk’ factors

Taking low doses of aspirin regularly may lower the risk of bowel cancer, particularly in people who lead less-healthy lifestyles, according to a new US study.

The findings of the study, which drew on the data of more than 100,000 men and women taking aspirin and who were followed up over 30 years, identified benefits across all groups but found the benefit was greatest among those with the least-healthiest lifestyles.

The findings could pave the way for more targeted prescribing of the drug according to a person’s risk profile.

Led by researchers at Mass General Brigham, which conducts the largest hospital-based research program in the US and is the oldest teaching affiliate of the Harvard Medical School, the study analysed the health data gathered in two key US investigations, comparing bowel cancer rates in those who took aspirin regularly with those who did not. Regular use was defined as taking either two or more standard-dose (325 mg) tablets per week or a daily low-dose (81 mg) of aspirin.

Published in JAMA Oncology, the study concluded: “The absolute reduction in CRC [bowel cancer] risk was more pronounced among those with an unhealthier lifestyle (i.e., higher body mass index, greater amount of smoking, higher alcohol intake, less physical activity, and poorer diet quality) compared with those with a healthier lifestyle.

“In contrast, the relative reduction in CRC risk associated with aspirin use was similar.”

The researchers added: “The findings of this study suggest that aspirin may be useful for [colorectal cancer] prevention for individuals with additional risk factors.”

US medical authorities had previously recommended daily low-dose aspirin to prevent cardiovascular events and bowel cancer in all adults aged 50 to 59 (the highest-risk age group for such cancer). However, in 2016, they withdrew the recommendation partly because of concerns about aspirin increasing the risk of gastrointestinal bleeding.

For their investigation, the researchers focused on two key studies – the Nurses’ Health Study (of women) and Health Professionals Follow-Up Study (of men) – with participants followed from an average age of 49.4 years.

“We sought to identify individuals who are more likely to benefit from aspirin to facilitate more personalised prevention strategies,” said co-senior author Andrew Chan, director of epidemiology for the Mass General Cancer Center and gastroenterology director of the Center for Young Adult Colorectal Cancer at Massachusetts General Hospital (MGH).

The study found overall that those people who regularly took aspirin had a colorectal cancer 10-year cumulative incidence of 1.98 per cent, compared with 2.95 per cent among those who did not take aspirin.

Participants deemed to have the least-healthy lifestyles had a 3.4 per cent chance of getting colorectal cancer if they did not take regular aspirin and a 2.12 per cent chance of getting colorectal cancer if they took aspirin regularly.

By contrast, in those with the healthiest lifestyle scores, the colorectal cancer rates were 1.5 per cent in regular aspirin-taking group and 1.6 per cent in the non-regular aspirin group.

The researchers explained: “This means that in the least-healthy group, treating 78 patients with aspirin would prevent one case of colorectal cancer over a 10-year period, while it would take treating 909 patients to prevent one case for the healthiest group.”

“Our results show that aspirin can proportionally lower the markedly elevated risk in those with multiple risk factors for colorectal cancer,” said Daniel Sikavi, lead author of the paper and a gastroenterologist at MGH. “In contrast, those with a healthier lifestyle have a lower baseline risk of colorectal cancer and, therefore, their benefit from aspirin was still evident, albeit less pronounced.”

One outcome of the study, according to co-senior author Long H. Nguyen, a physician investigator at MGH, could be that “healthcare providers might more strongly consider recommending aspirin to patients who have less-healthy lifestyles”.

The lifetime risk of developing bowel cancer is 1 in 16.

Bowel cancer is Australia’s second deadliest cancer.

Previous studies have found evidence to suggest aspirin can reduce the production of pro-inflammatory proteins, known as prostaglandins, that can promote the development of cancer.

The MGH study noted that several different mechanisms might be involved in aspirin’s protective role, but “identifying those who would benefit most from aspirin remains essential due to the potential adverse effects of chronic aspirin use”.