It has been suggested that regular use of aspirin can reduce the chances of developing colorectal cancer but now it has also been found that it reduces mortality in those who do have the cancer.
Daily low dose aspirin is often used to prevent heart attacks in people who have already had one or who are at high risk of having their first. It is also used after some forms of stroke and there is growing evidence of its use to prevent dementia and some cancers.
Scientists at Massachuettes General Hospital and Harvard Medical School in Boston studied 1,279 men and women with colorectal cancer at various stages.
Dr Andrew Chan, writing in the Journal of the American Medical Association said that aspirin is likely to help prevent colorectal cancer because it blocks the COX-2 enzyme which encourages inflammation and cells to multiply. The enzyme is produced in large quantities in many colorectal cancers.
The group was followed up for an average of 11.8 years and the number of deaths was collected in people who used various doses of aspirin and those who did not take the drug at all, including deaths from colorectal cancer.
In the study people who said that they used a standard aspirin tablet (325 mg) at least two times a week were classified as aspirin users.
Overall 88 per cent of patients who used aspirin were still alive five years after their cancer diagnosis compared with 83 per cent of those who did not use aspirin.
After ten years 74 per cent of aspirin users were still alive compared with 69 per cent of non-users.
The analysis was repeated looking at whether patients used aspirin before they diagnosis or after or both.
The authors said the cancer deaths were reduced significantly only in those who took up using aspirin after their cancer was diagnosed. There was little effect in those who had used aspirin throughout.
Dr Chan wrote: "Notably, among participants who used aspirin before diagnosis, continuation of aspirin use after diagnosis did not appear to influence survival. This suggests the possibility that tumours that initially developed despite exposure to aspirin may be less susceptible to any potential effect of aspirin on tumour progression."
This theory is backed up by other findings in the study which found aspirin had the strongest effect on cancers with excessive amounts of COX-2 enzyme which is suppressed by the drug.
The research paper said: "In the current study, we found that aspirin use after diagnosis was associated with lower colorectal cancer?specific mortality among individuals with COX-2–positive tumour but not COX-2–negative tumours. This supports the hypothesis that COX-2–positive tumours may be relatively sensitive to the anticancer effect of aspirin, whereas COX-2–negative tumours may be relatively aspirin-resistant.
"Moreover, it potentially explains the observation that the benefit of postdiagnosis aspirin use on patient survival was not apparent among patients who used aspirin prior to cancer diagnosis."
The results showed patients who had COX-2 positive tumours and were regular aspirin users after diagnosis of their cancer were 61 per cent less likely to die from the disease compared with patients who had COX-2 negative cancers.
Dr Chan wrote that the finding suggest that aspirin could be targeted at for colorectal cancer patients whose tumour is COX-2 positive and not at those whose tumour is negative.
However, he warned that further research is needed before aspirin can be recommended for patients with COX-2 positive tumours because of the side-effects of the drug which can include stomach bleeding.
In an accompanying editorial by Dr Alfred Neugut, of Columbia University, New York, said because the benefits of aspirin were in seen in patients who received standard chemotherapy to treat the cancer as well as in those who did not, it suggests the drug can be used alongside standard therapy.
He said: "Thus, aspirin may have the potential to be useful as adjuvant therapy not just for locally advanced disease but for early-stage patients as well. Further studies are needed to confirm and extend these findings."
© THE Telegrap Group London 2009