Beneficial long-term effect of aspirin on colorectal cancer incidence, mortality

January 01, 0001

Beneficial long-term effect of aspirin on colorectal cancer incidence, mortality

High-dose aspirin (greater than or equal to 500 mg daily) reduces long-term incidence of colorectal cancer, but adverse effects might limit its potential for long-term prevention. The long-term effectiveness of lower doses (75—300 mg daily) is unknown. The researchers from the UK, Sweden and The Netherlands assessed the effects of aspirin on incidence and mortality due to colorectal cancer in relation to dose, duration of treatment, and site of tumour. They followed up four randomised trials of aspirin versus control in primary (Thrombosis Prevention Trial, British Doctors Aspirin Trial) and secondary (Swedish Aspirin Low Dose Trial, UK-TIA Aspirin Trial) prevention of vascular events and one trial of different doses of aspirin (Dutch TIA Aspirin Trial) and established the effect of aspirin on risk of colorectal cancer over 20 years during and after the trials by analysis of pooled individual patient data. In the four trials of aspirin versus control (mean duration of scheduled treatment 6·0 years), 2.8% of 14,033 patients had colorectal cancer during a median follow-up of 18.3 years.

Allocation to aspirin significantly reduced the 20-year risk of colon cancer (incidence hazard ratio, HR, 0.76; mortality HR 0.65), but not rectal cancer (0.90; 0.80). Where subsite data were available, aspirin reduced risk of cancer of the proximal colon (0.45; 0.34), but not the distal colon (1.10; 1.21). However, benefit increased with scheduled duration of treatment, such that allocation to aspirin of 5 years or longer reduced risk of proximal colon cancer by about 70% (0.35; 0.24) and also reduced risk of rectal cancer (0.58; 0.47). There was no increase in benefit at doses of aspirin greater than 75 mg daily, with an absolute reduction of 1.76% in 20-year risk of any fatal colorectal cancer after 5-years scheduled treatment with 75—300 mg daily. However, risk of fatal colorectal cancer was higher on 30 mg versus 283 mg daily on long-term follow- up of the Dutch TIA trial (odds ratio 2.02, not significant).

The researchers concluded: "Aspirin taken for several years at doses of at least 75 mg daily reduced long-term incidence and mortality due to colorectal cancer. Benefit was greatest for cancers of the proximal colon, which are not otherwise prevented effectively by screening with sigmoidoscopy or colonoscopy."

Such long-term data appears reassuring, especially considering deaths from other causes eg bleeds.

For the full abstract, click here.

The Lancet published online 22 October 2010 © 2010 Elsevier Limited
Long-term effect of aspirin on colorectal cancer incidence and mortality: 20-year follow-up of five randomised trials. Correspondence to Prof Peter Rothwell: [email protected]

Category: D. Digestive. Keywords: aspirin, effects, long-term, colorectal, cancer, incidence, mortality, follow-up of randomised trials, journal watch.
Synopsis edited by Dr Stephen Wilkinson, Melbourne, Australia. Posted on Global Family Doctor 12 November 2010

Pearls are an independent product of the Cochrane primary care group and are meant for educational use and not to guide clinical care.