Cancer

There is increasing evidence that regular use of aspirin may reduce the risk of developing certain cancers. For most cancers, the evidence comes from observational studies that cannot prove a causal link but nonetheless provide important information that can be tested more rigorously in prospective randomised trials. One example in this category is breast cancer.

• Aspirin Foundation Position Paper:
Breast cancer prevention

There is stronger evidence that aspirin may prevent colorectal cancer (bowel cancer). This possibility was originally raised in observational studies and was subsequently tested in prospective randomised trials. It has now been shown that regular consumption of aspirin reduces the risk of colorectal cancer by about 40 percent after at least 5 years' use.

• Aspirin Foundation Position Paper:
Colorectal cancer prevention

The mechanism by which aspirin may reduce cancer risk is probably the inhibition of the enzyme cyclo-oxygenase 2 (COX-2): a recent study from the United States showed that aspirin reduced the risk of developing colorectal tumours that over-express COX-2 but not of tumours that do not have increased expression of this enzyme (N Engl J Med 2007; 356:2131-42; http://content.nejm.org/cgi/content/abstract/356/21/2131).