A pooled analysis of five trials with 20 years of follow up suggests that taking a low dose of aspirin may cut the risk of developing and dying from colon cancer, the second most common cancer in developed countries after lung cancer.
The researchers found that it reduced the incidence of colon cancer by 24 per cent and deaths by 35 per cent.
They said their findings may tip the balance in favour of using aspirin to prevent colon cancer, reported Reuters.
Peter Rothwell, Professor of Clinical Neurology at the University of Oxford, and also of Oxford’s John Radcliffe hospital, both in the UK, and colleagues, presented the findings of their analysis in the 22 October issue of The Lancet.
Colorectal cancer has a lifetime risk of 5%; every year about 1 million people discover they have the disease and 600,000 die from it.
In their analysis, Rothwell and colleagues analyzed five pooled randomized trials that assessed the effect of aspirin on incidence and mortality of colorectal cancer, with particular focus on dose, duration of treatment and tumor site.
Previous studies have already shown that high-dose aspirin (500 mg and more a day) reduces long-term incidence of colorectal cancer, but the risk of adverse effects such as gastro-intestinal bleeding “might limit its potential for long-term prevention”, wrote the authors.
For the study, Rothwell and colleagues followed up five trials (done in the UK, Sweden and Holland) that were primarily interested in the effects of aspirin on cardiovascular outcomes but they were able to track colorectal cancer incidence and deaths through cancer registries and death certificates.
They then pooled individual patient data and analyzed the effect of doses of at least 75 mg daily of aspirin on risk of colorectal cancer over 20 years during and after the trials.
The results showed that:
- In four trials of aspirin versus control (average duration of scheduled treatment was 6 years), 2.8 per cent of over 14,000 patients had colorectal cancer over a median follow-up of 18.3 years.
- Those on aspirin had a 24 per cent reduction in risk of colon cancer (incidence hazard ratio HR = 0.76, 95% confidence interval CI = 0.60 – 0.96, p=0.02) and the risk of death also went down by 35 per cent (0.65, 0.48-0.88, 0.005).
- However, rectal cancer did not show such a drop (0.90,0.06-1.30, 0.58 for incidence and 0.80, 0.50-1.28, 0.35 for mortality).
- Where tumor site data was available, it appeared that aspirin reduced risk of cancer of the proximal colon but not the distal colon.
- The benefit increased with scheduled duration of treatment, such that being on aspirin for 5 years or more reduced the risk of proximal colon cancer by about 70 per cent, and reduced rectal cancer risk.
- There was no benefit increase at doses higher than 75 mg a day.
- In the Dutch trial, that tested different doses, the risk of fatal colorectal cancer was higher on 30 mg a day than 283 mg a day.
The authors concluded that:
“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,” they noted.
This news is likely to have a mixed reception. Some doctors may be reluctant to promote the aspirin route as a way to prevent colon cancer because of the associated risks, while others may be attracted by the relatively cheap alternative that the drug offers, especially if they sympathize with patients who wish to avoid the discomfort and embarassment of invasive tests.
In an accompanying editorial, Drs Robert Benamouzig and Bernard Uzzan, of Avicenne Hospital in Bobigny, France, said the study had limitations in that cancer was not the primary outcome studied in the trials, and there was not enough data on aspirin-related deaths.
Also, the patients were mostly men with cardiovascular risks, so the findings can’t be generalized to other populations like women and people without those risks.
However, they said the study was very “interesting”, particularly in relation to high-risk patients.
“Long-term effect of aspirin on colorectal cancer incidence and mortality: 20-year follow-up of five randomised trials.”
Peter M Rothwell, Michelle Wilson, Carl-Eric Elwin, Bo Norrving, Ale Algra, Charles P Warlow, Tom W Meade.
DOI: 10.1016/S0140-6736(10)61543-7
Additional source: Reuters.
Written by: Catharine Paddock, PhD