Guidelines advise considering aspirin for primary prevention of colorectal cancer – with caveats. Now a new study offers insights on which patients may benefit most…

Guidelines recommend considering low-dose aspirin for people aged 50 to 70 with an average risk of colorectal cancer, unless they have contraindications to aspirin use – but although the recommendation was added to clinical practice guidelines in 2017 it hasn’t been widely taken up.

What do the guidelines recommend?

• Consider a low dose of 100–300 mg per day for at least 2.5 years in people aged 50-70 with average risk, unless aspirin is contraindicated. 

• In people over age 70, benefit for cancer prevention is only evident 10 years after the aspirin is initiated, so life expectancy needs to be factored in.   

• The benefits for colorectal cancer risk reduction are less clearcut in women over 65, but that limited data suggests the benefits may outweigh the harms in those who also have CVD risk factors.  

Aspirin should be avoided in people with uncontrolled hypertension, as well as “current dyspepsia, any history of peptic ulcer, aspirin allergy, bleeding diathesis, an increased risk of gastrointestinal haemorrhage (such as associated with use of oral anticoagulants or antiplatelet agents), or renal impairment,” the guidelines note. See the practice points in section 2.1.2 of the guidelines for more information and practice tips. 

Limitations of the research

“Aspirin use for this indication is not yet widespread in clinical practice, and there remain several unresolved issues,” says gastroenterologist, hepatologist and addiction medicine physician Dr Emily Nash, Staff Specialist at the Royal Prince Alfred Hospital’s AW Morrow Gastroenterology and Liver Centre and Clinical Associate Lecturer, University of Sydney Medical School.  

“Clinical trial data on which the recommendations were based was mostly derived from post hoc analyses of cardiovascular prevention trials, which predominantly involved men (92%), and none of the trials had colorectal cancer as the primary endpoint,” she says.  

“The optimal aspirin dose and target age range have not yet been identified,” she adds.   

Aspirin may be more beneficial in those with less healthy lifestyles

A recent study which followed 107,655 men and women for over three decades has shed more light on who may benefit most. 

The prospective cohort study published in JAMA Oncology found that aspirin led to a greater absolute reduction in colorectal cancer risk in those with less healthy lifestyles than those with healthier lifestyles – which factored in body mass index, alcohol intake, physical activity, diet and smoking.  

Body Mass Index and smoking were the lifestyle factors associated with the biggest absolute risk reduction. 

Those with the least healthy lifestyles experienced the greatest risk reduction, and those with the healthiest lifestyles experienced the least. 

The authors say their findings “suggest that lifestyle risk factors may be useful to identify individuals who may have a more favourable risk-benefit profile for cancer prevention with aspirin.” 

Address known risk factors

This highlights the importance of addressing known risk factors, experts stress.  

Almost half of all bowel cancers in Australia are associated with modifiable risk factors such as poor nutrition, high body mass, physical inactivity, risky alcohol consumption and smoking, says cancer epidemiologist Professor Karen Canfell, Chair of the Cancer Council’s Screening and Immunisation Committee, who has led evaluations of cancer screening approaches for government agencies across several countries.  

“Avoiding these risks would have a huge impact on reduced bowel cancer incidence,” she says.  

The guidelines also note that:

• People with Lynch Syndrome carrier status should begin aspirin when they start colonoscopy screening, usually age 25  

• Helicobacter pylori is associated with increased gastrointestinal side effects from aspirin; breath testing and treatment for those who test positive “can be considered.”  

For more information:

Clinical practice guidelines for the prevention, early detection and management of colorectal cancer| Chemopreventive candidate agents (magicapp.org)