Aspirin prophylaxis for colorectal cancer?

A recent article in The Lancet has provided additional information about the use of aspirin for cancer prevention, especially colorectal cancer (Rothwell PM et al. Lancet 2012; published online March 21. DOI: 10: 1016/S0140-6736 (11)61720-0).  In the commentary on this article (DOI: 10: 1016/S0140-6736 (11)61654-1), the potential benefits of aspirin are placed into context and previous studies are reviewed.  In short, the data from a number of studies suggest that aspirin lowers the risk of cancer.

In Rothwell’s study, which pooled data from 51 randomized trials, aspirin at any dose reduced the risk of non-vascular death by 12% and cancer death by 15%.   Benefit was seen within 3 years for high-dose (>300 mg/day) and after 5 years for low doses (<300 mg).  The cumulative numbers of patients in the reviewed studies was approximately 40,000 in each arm.  These studies were divided and examined under separate categories to assess primary prevention for vascular events and to assess effects on cancer deaths.

Yet, these encouraging results though have not been seen in several large randomized trials; the editorial notes that “the Women’s Health Study (WHS) of 39,876 women treated with alternated day 100 mg aspirin over 10 years and the Physicians’ Health Study (PHS) of 22,071 men treated with alternate-day 325 mg aspirin for 5 years.  After 10-12 years of folllow-up, aspirin was not associated with reduced risk of colorectal cancer.”  In addition, as noted in previous post, ( Who needs aspirin?/Arch Intern Med 2012; 119: 112-8) a large study with over 100,000 patients also did not show reduction in mortality from vascular or non-vascular events.

Whether alternate-day dosing of aspirin (in WHS and PHS studies) undermines its efficacy in preventing cancer is not clear.  Until more data are available, aspirin for chemoprevention is best-suited for those with increased cancer risk (eg. history of colorectal cancer & hereditary cancer syndrome) and low risk of GI bleeding.  Rates of bleeding due to aspirin are about 4% per year and for serious bleeding about 2% per year. In addition, other adverse effects, including macular degeneration, have been reported with aspirin use (Ophthalmology 2012; 119: 112-8).

Additional references:

  • Link to pdf copy of cited article:http://extremelongevity.net/wp-content/uploads/asa-ca.pdf
  • -Lancet 2011; 377: 31-41. Aspirin effect on cancer mortality -decreased by 30-40% (esophageal, gastric, pancreatic, colorectal)
  • -Lancet 2010; 376: 1741 – 1750. Long-term effect of aspirin on colorectal cancer incidence and mortality: 20-year follow-up of five randomised trials. Lowers risk of colon Ca.
  • -JAMA 2009; 302: 649. Aspirin use likely increases survival after dx of colon cancer.
  • -Gastro 2010;138: 2012. Commentary on aspirin for decreasing risk after diagnosis of colon cancer.
  • -NEJM 2007; 356: 2131, 2195. Aspirin can decrease high-expressing COX-2 colon adenoca; not recommended as routine prophylaxis at this time

1 thought on “Aspirin prophylaxis for colorectal cancer?

  1. Pingback: Thiopurines associated with reduced risk of colon cancer | gutsandgrowth

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