low-dose aspirin

Millions of people take low-dose aspirin to prevent heart attacks and strokes. Researchers determine whether a new use of low-dose aspirin can help in colorectal cancer prevention.

Colorectal rectal is a very common cancer and the second most diagnosed cancer in Canada with roughly 27,000 new cases diagnosed annually.1 Follow-up studies in patients on low-dose aspirin have demonstrated the long-term protective effects of the drug against colorectal cancer emergence and death from the disease.2 Additionally, aspirin was found to reduce the risk of colorectal adenomas, which are benign tumors or polyps that can be the precursors of cancerous lesions, in individuals with a history of such lesions.3 However, these studies did not take the effects of confounding factors, such as diet, alcohol consumption, or the pre-trial intake of aspirin by the control group, into account.

A recent study, which published its findings in BMC Cancer, 4 investigated the effects of low dose-aspirin on the risk of developing colorectal cancer. The study examined the dependence of this risk on aspirin dosage, the duration of aspirin intake, the disease for which the drug was prescribed. Additionally, the study examined the link between aspirin use and the stage of colorectal carcinoma at diagnosis, tumor site, and fatality status.

Data for the analysis was obtained from The Health Improvement Network (THIN) database, which contains primary care data for a small but significant section of the UK population. Secondary care data was also available for a significant proportion of the patients in the THIN database. A total of 170,336 patients were included in the study. They were between 40 and 80 years of age, registered with general practice for at least two years with at least one year of computerized prescription history, had at least one health encounter in the previous three years, and were new users of low-dose aspirin.

Each patient in the low-dose aspirin group was matched for age, sex, and the number of primary care provider visits with an individual not taking aspirin. The latter group of individuals formed the control group. Patients in both groups were followed until they were diagnosed with colorectal or some other form of cancer turned 90 years of age or passed away, or until the end of the study period, which was on December 31, 2011.

An analysis of the data showed that an intake of aspirin cuts the risk of colorectal cancer incidence by 34%. The decrease in risk was observed across all age groups and was independent of dosage, gender, tumor site, indication, or fatality status. Low-dose aspirin also reduced the risk of cancer progression in patients with pre-existing colorectal cancer. A reduced risk was observed for Dukes Stages B to D of colorectal cancer during the first year of aspirin therapy, while a reduced risk for Dukes Stage A colorectal cancer was observed after five years of aspirin therapy.

These findings add to the growing body of evidence that intake of aspirin can cut the risk of developing colorectal cancer, which is another new use of low-dose aspirin. As for other cancers, while some studies indicate a lowered risk for melanoma, pancreatic cancer, and ovarian cancer with aspirin intake, other studies do not support these findings.

Finally, it is important to note that aspirin may increase the risk of gastrointestinal bleeding, and the risks versus benefits may vary from individual to individual. Therefore, self-medication is not advised. It is best to consult with a primary care provider to determine if low-dose aspirin therapy is appropriate for you.

Written by Usha B. Nair, Ph.D.


  1. Canadian Cancer Society. Colorectal cancer. http://www.cancer.ca/en/cancer-information/cancer-type/colorectal/statistics/?region=on. Accessed: September 16, 2017.
  2. Rothwell PM, Wilson M, Elwin CE, Norrving B, Algra A, Warlow CP, Meade TW. Long-term effect of aspirin on colorectal cancer incidence and mortality: 20-year follow-up of five randomised trials. Lancet. 2010 Nov 20;376(9754):1741-50. doi: 1016/S0140-6736(10)61543-7. Epub 2010 Oct 21. PubMed PMID: 20970847.
  3. Cole BF, Logan RF, Halabi S, Benamouzig R, Sandler RS, Grainge MJ, Chaussade S, Baron JA. Aspirin for the chemoprevention of colorectal adenomas: meta-analysis of the randomized trials. J Natl Cancer Inst. 2009 Feb 18;101(4):256-66. doi: 10.1093/jnci/djn485. Epub 2009 Feb 10. PubMed PMID: 19211452.
  4. García Rodríguez LA, Soriano-Gabarró M, Bromley S, Lanas A, Cea Soriano L. New use of low-dose aspirin and risk of colorectal cancer by stage at diagnosis: a nested case-control study in UK general practice. BMC Cancer. 2017 Sep 7;17(1):637. doi: 10.1186/s12885-017-3594-9. PubMed PMID: 28882113; PubMed Central PMCID: PMC5590216.

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