Aspirin prevents colon cancer

We have previously summarized strategies to reduce the risk of colon cancer. Briefly, these include increasing physical activity, avoiding weight gain, reducing red meat consumption, limiting alcohol and following screening recommendations.
Aspirin has been regularly recommended by the US Preventive Services Task Force (USPSTF) for the prevention of cardiovascular disease in men and women (2009). Men are advised to take aspiring daily starting at age 45. Women are advised to start taking aspirin regularly at age 55. The recommendation regarding aspirin for colon cancer prevention stops short of advising use (2007). The USPSTF and more recent review articles advise that more research is needed to determine appropriate dose for colon cancer prevention. Furthermore, primary care providers are advised to assess and discuss the risks and benefits of aspirin with their patients. The well-documented risk of aspirin use is gastrointestinal bleeding (Huang et al., 2011). The current recommendation cautioning against use for colon cancer prevention appears at odds with the ongoing recommendations for cardiovascular prevention and with the evidence that aspirin use reduces mortality from colon cancer.
Substantial evidence shows that aspirin use in randomized controlled trials for cardiovascular disease shows reduced colon cancer deaths over 20 or more years of follow-up. Data from 5 randomized controlled trials shows a 25 percent reduction in colon cancer incidence over 20 years and a 35 percent reduction in colon cancer mortality (Rothwell et al., 2010). Parallel data from prospective cohort studies in which aspirin use has been recorded and participants followed over time and monitored for development of colon cancer or death from colon cancer show the same magnitude of risk reduction (Zhang et al., 2011).

Now a new study of high risk patients, known to carry genetic changes from birth that put them at increased risk of colon cancer shows that use of aspirin for 5 years reduces colon cancer incidence. Patients with Lynch syndrome, the major form of hereditary colon cancer – were randomized to aspirin or placebo and followed for a mean of 55 months. After using aspirin at a does of 600 mg per day for 2 years participants had a 60 percent reduction in risk of colon cancer compared to those randomized to placebo pills (Burn et al., 2011). 
Given this dose has been shown to protect against colon cancer in other randomized trials followed for cancer mortality, the debate about dose and mechanism should cease – these can continue as academic pursuits. We owe it to the population to get beyond these concerns for recommendations of proven effective prevention strategies.
Further evidence in support of cancer prevention recommendations for aspirin come from the assessment of total cancer mortality in the patients followed from randomized trials. Over 25,000 patients were followed and 674 cancer deaths were confirmed.   Benefits of reduced cancer deaths were only evident after 5 or more years of follow-up. Reductions were significant for total cancer and for gastrointestinal cancers. Benefit increased with the duration of treatment (Rothwell et al., 2011).
In sum, aspirin use substantially reduces colon cancer incidence and death due to colon cancer. This benefit should be added to the discussion of risks and benefits when men and women consider aspirin for prevention of cardiovascular disease.

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