Bowel cancer is the third most common cancer. There are two effective preventive methods. [See reference 1 ]

Screening: A test for blood in the faeces is done first and if this is positive then the bowel is examined by a flexible tube (colonoscope). This procedure reduces the risk of death from bowel cancer by about 30-40%. [See references 2 and 3 ]

Aspirin: Taking a small daily dose of aspirin reduces the risk of bowel cancer by about 40%. [See references 4 and 5 below ]

Screening PLUS aspirin: Taking a small daily dose of aspirin, and having regular screening tests is likely to be the most effective strategy for the reduction of bowel cancer! [See reference 6 and 7 ]

Over the lifetime of an average person in the UK, about six people will develop bowel cancer, and this rate seems to be increasing steadily over time. [See reference 1] Almost all cases occur over the age of about 50 years, and the risk increases rapidly with advancing age.

The bowel is a long passage, and it can be described as a beginning half (the proximal colon) and an end half (the terminal or distal colon). Screening with a flexible tube is relatively simple, but its effectiveness is largely confined to the distal part of the bowel. On the other hand, the major benefit of aspirin is in reducing growths is in the first half of the bowel, the proximal colon. [See reference 5 and 6 below]

Both screening of the bowel (colonoscopy), and low-dose aspirin are beneficial, but both have risks. Both can cause bleeding, screening from the bowel, aspirin from the stomach. Each however has also a more serious danger. Rarely, the bowel wall can be damaged and even perforated during screening ,[See reference 8 below] and rarely aspirin can lead to a haemorrhagic stroke. These events are however rare and are more than outweighed by the benefit each confers. [See sourxces 6 and 7]

Everyone should therefore accept bowel screening if it is offered, and everyone aged over about 50 should think seriously about taking a small dose of aspirin (70-100 mg daily…. but do read the section on ‘Aspirin and Bleeding’ first.


  1. National Institute for Health and Care Excellence. The diagnosis and management of colorectal cancer: full guideline. November 2011.
  2. Outcomes of the bowel cancer screening programme (BCSP) in England after the first 1 million tests. Gut 61(10), 1439-46 (2011).
  3. Once only flexible sigmoidoscopy screening in prevention of colorectal cancer: a multicentre randomised controlled trial. Lancet 375, 1624-33 (2010).18,19,20,21
  4. The role of low-dose aspirin in the prevention of colorectal cancer. Expert Opin Ther Targets. 16 Suppl 1, S51-62 (2012).
  5. Effects of regular aspirin on long-term cancer incidence and metastasis: a systematic comparison of evidence from observational studies versus randomised trials. Lancet 13, 518-27 (2012).
  6. Colorectal Cancer Prevention: screening and the role of aspirin. Colorectal Cancer 2013;2(5):429-39
  7. Primary prevention of colortectal cancer with low-dose aspirin in combination with endoscopy: a cost effective analysis. Gut 2012;61:1172-9.
  8. Progress and challenges in colorectal screening and surveillance. Gastroenterology 138, 2115-26 (2010).
  9. Aspirin, salicylates and cancer. Lancet 2009;373:1301-9

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