Aspirin & cancer

A small daily dose of aspirin is associated with large reductions in cancer. Estimates of the reduction vary according to the cancer, but overall, aspirin will prevent cancer in three or four people in every hundred. [see References 1-7 below].

Considering both heart disease, stroke and cancer together, ten years of low-dose aspirin is likely to lead to reductions of these diseases in about 9% in men and about 7% in women.

These benefits of aspirin far outweigh the dangers of bleeding attributable to low-dose aspirin. [see References 8-10 below].

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A large number of long-term trials have shown that the occurrence of cancer is reduced in the people who take aspirin. [see References 1-7 below].

For example: in an overview of seven trials based on 23,535 people, aspirin taking for five years was associated with a reduction in new cancers of just over 30%. [See reference 4 below] Another pooled analysis of 34 trials showed that over a third fewer cancer deaths occurred after five years in the people who had taken daily aspirin. [See reference 5 below] Yet further confirmation of benefit has come from a very large study of women in the USA, in which bowel cancer was reduced by just over 20% in women who took aspirin. [See reference 8 below].

An especially valuable trial was conducted in patients with a genetic condition which carries a very high risk of bowel cancer. There were about half the number of cancers in patients who took aspirin for at least two years compared to patients in the ‘placebo’ group. [See reference 7 below].

All the evidence given so far comes from carefully conducted trials in which aspirin has been given to only half a group of subjects, chosen at random.

Evidence showing a reduction by aspirin in cancer goes back to at least 1968. The early studies showed both a reduction in the spread of cancer (metastatic spread) and an increase in survival with cancer. [See reference 12 below] As early as 1997 an international group of experts concluded that a protective relationship between aspirin taking and cancer had been established [See reference 13 below] and in 2009 a wide ranging review of evidence from a variety of references – botanical, animal, human and cellular – supported an effect on cancer with remarkable consistency. [See reference 14 below].

Science advances in a number of ways one of which is the fulfilment of predictions. Early ‘test-tube’ work on aspirin identified protective mechanisms within cells by which aspirin might reduce cancer and this led to the prediction that a reduction in cancer would be seen clinically only after perhaps five or ten years of aspirin taking. This prediction has been abundantly fulfilled in observational and randomised studies – the protective effect of taking aspirin becomes clinically obvious only after about five years of aspirin taking, and the benefit increases thereafter. [See reference 3-7 below].

Doctors and health authorities talk about the ‘cost-effectiveness’ of drugs and other treatments. For doctors and patients, ‘cost’ relates to the possible harms of the treatment, while for health authorities ‘cost’ includes the financial cost. However it is evaluated, aspirin is highly ‘cost-effective’! [See reference 10-12 below].

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  2. Effect of aspirin on long-term risk of colorectal cancer: consistent evidence from randomised and observational studies. Lancet 2007;12:1603-13.
  3. Long-term effect of aspirin on colorectal cancer incidence and mortality: 20-year follow-up of five randomised trials. Lancet 2010;376:1741-50.
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  7. Long-term effect of aspirin on cancer in carriers of hereditary colorectal cancer : an analysis from the CAPP2 randomised trial. Lancet 2010;377:2081-7.
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  9. Estimates of the benefits and harms of prophylactic use of aspirin in the general population. Ann Oncol;2014:
  10. The role of aspirin in cancer prevention. Nat Rev. Clin. Oncol. 2012;9(5):259-267.
  11. Effect of including cancer mortality on the cost-effectiveness of aspirin for primary prevention in men. J Gen Intern Med May 2013 (epub ahead of print)
  12. Primary prevention of colorectal cancer with low-dose aspirin in combination with endoscopy: a cost effective analysis. Gut. 2012;61(8):1172-1179..
  13. Anti-metastatic effects associated with platelet reduction. Proc Natl Acad Sci USA. 1968;61:46-52.
  14. IARC Handbooks of cancer prevention. Non-steroidal anti-inflammatory drugs. Vol 1. International Agency for Research on Cancer. Lyon. 1997
  15. Aspirin, salicylates and cancer. Lancet 2009;373:1301-9