Cancer latest info, news, treatment, advice- Mainstream and alternative cancer cures

14 May 2007

Daily use of aspirin can prevent bowel cancer, reported six newspapers (11 May 2007). The articles reported on research which found a link between aspirin use and a reduced risk of colorectal cancer. This finding was based on an analysis of long-term aspirin users so may not apply to the general population.

*

Six newspapers (1-6) reported that taking 300 mg of aspirin daily for five years could reduce the risk of developing bowel cancer by 74% in the 10 to 15 years after starting treatment.
*

The articles are based on research published in the Lancet (7). This was an analysis of two aspirin trials conducted in the 1980's which compared aspirin (300 mg, 500 mg or 1200 mg a day) and placebo or no aspirin. All deaths and cancer cases for up to 23 years were obtained from National Registries and compared between the aspirin and no aspirin groups. The risk of colorectal cancer was reduced by 26% overall; 37% for those taking aspirin for at least five years; and by 74% after 10 to 15 years for those who complied with treatment. The link between 300 mg of aspirin and reduced colorectal cancer risk for at least five years was also seen in a supporting systematic review of observational studies.
*

The newspapers reported the research fairly accurately with all concentrating on the 74% reduction in risk. However this was based on a small subgroup of only those participants who complied with the aspirin treatment for at least five years and the number of colorectal cancer cases was low. None of the reports pointed out that the trials were not designed to assess colorectal cancer and were of specific populations (men or people with a minor stroke) so the findings may not apply to the general population.

Evaluation of the evidence base for the effect of aspirin on the risk of colorectal cancer
Where does the evidence come from?

An analysis of two randomised trials and a systematic review conducted by Professor Peter Rothwell and colleagues from the Stroke Prevention Research Unit at the Radcliffe Infirmary, Oxford.
What were the authors' objectives?

The objectives were to assess the longer-term effect of aspirin on the incidence of colorectal cancer.
What was the nature of the evidence?

The research had two parts: analysis of data from two randomised controlled trials conducted in the UK between 1978 and 1985; and a systematic review of observational studies. One trial, the British Doctors Aspirin Trial, assessed 5139 British male doctors with no history of peptic ulcer, stroke or heart attack. Participants received aspirin treatment for five or six years and were followed up until 2001 for the occurrence of cancer and/or death. The UK Transient Ischaemic Attack Aspirin Trial (UK-TIA) assessed 2449 people who'd had a recent (within three months) transient ischaemic attack or minor stroke, who were over 40 with no history of aspirin intolerance, alcoholism, chronic renal failure or peptic ulcers. Follow-up data for the incidence of cancer and death were obtained up to the end of 2005. The main outcome was the incidence of colorectal cancer, results for other types of cancer were also analysed.

The systematic review assessed published observational studies for the association between aspirin or NSAID use and the risk of colorectal cancer. Nineteen case-control and 11 cohort studies were included.
What interventions were examined in the research?

The Doctors trial compared 500 mg of aspirin a day with no aspirin. The UK-TIA trial had three arms: 1200 mg of aspirin a day; 300 mg a day; and placebo. The two aspirin arms of this trial were combined for the analysis. Duration of treatment varied from one year to more than seven years in the UK-TIA trial and in the Doctors trial it was five or six years.
What were the findings?

In the pooled analysis of data from both trials, daily aspirin use was associated with a statistically significant reduction of 26% in the incidence of colorectal cancer, with 2.5% (n=129/5061) of aspirin and 3.4% (n=87/2527) of control participants developing colorectal cancer. For those participants who took aspirin for at least five years, the reduction in the incidence of colorectal cancer was 37%. The largest effect of aspirin was seen 10 to 14 years after randomisation in the subgroup of participants who were treatment compliant (taking treatment for at least 50% of follow-up assessments) for at least five years, with a reduction in incidence of 74%. Aspirin use did not have any affect on the incidence of other types of cancer.

The systematic review found an association between aspirin use and a reduced risk of colorectal cancer but only for daily dose of 300 mg or more. Results were inconsistent for lower or less frequent doses.
What were the authors' conclusions?

The authors concluded that randomised trials show that taking at least 300 mg of aspirin a day for five years may be effective for the primary prevention of colorectal cancer, with benefits being seen after 10 years. Lower or less frequent doses might be less effective but further follow-up of trials of low-dose aspirin are needed.
How reliable are the conclusions?

The main results of this research are based on additional analyses of long-term follow-up data from two randomised controlled trials. Earlier results from both trials have previously been published (8, 9). Both appear to be large, well-conducted trials although only one used placebo tablets, but as the outcome was cancer incidence, knowledge of the treatment received is unlikely to directly affect any results. There were differences in the patient populations and only limited details of patient characteristics were reported, with no details of possible risk factors for cancer. The analysis methods appeared appropriate and accounted for the fact that data came from two different trials. Cancers were coded using standard classifications by staff that were blind to treatment allocation.

The systematic review used methods to ensure that the relevant studies were located and data was selected and analysed in an unbiased manner. This appears to be a well-conducted piece of research, although there are limitations due to the different patient populations. There was also no reporting of side-effects of aspirin use, as long-term use is not recommended by doctors because of possible internal bleeding. The authors do discuss some limitations mainly that the trials were not designed to assess colorectal cancer and both were conducted before colonoscopic screening was available which may now prevent some cancers.

http://www.library.nhs.uk/rss/newsAndRssArticle.aspx?uri=http://www.libr...