Bowel Cancer

Like Sir Richard, most people are sceptical when they first hear about the possibility that aspirin might protect against bowel cancer. But there is good reasoning behind the proposal - and the evidence, from a study of cases of colorectal cancer in American nurses, is compelling.

Some cases of bowel cancer are preceded by the development of multiple polyps - and aspirin may help in some way to prevent them or to stop them from becoming malignant. There is also evidence that bowel cancer may be linked with high levels of prostaglandins in the bowel wall - and aspirin may reduce them. It is also possible that aspirin is a "free radical scavenger" in the bowel - and free radicals are waste products of metabolism that have been linked with the development of cancer.

Whatever the theory behind the action of aspirin on the bowel, the United States Nurses' Study has produced remarkable evidence supporting aspirin's protective effect against cancer.

It followed nearly 90,000 nurses since 1976. At the time of the report in 1995, 501 had developed colorectal cancer. The nurses who had regularly reported aspirin use in questionnaires completed in 1980, 1982 and 1984 had a relative risk of developing the disease compared to the non-users of 0.72 in 1985, 0.61 in 1990 and 0.55 in 1992. In other words, the longer they used aspirin (regular use was defined as 4-6 tablets a week) the less likely they were to develop bowel cancer. The study was published in the New England Journal of Medicine (1995;333: 656-658).

The Journal asked Dr Aaron Marcus, of the New York Veterans Affairs Medical Center, to write an editorial on the study. He advised that "People at risk from colorectal cancer - those with inflammatory bowel disease, breast, ovarian or endometrial cancer; or a previous adenoma or large bowel cancer - should take a single aspirin tablet of 325mg every other day, barring any contraindication. Those with a family history of colorectal cancer or adenoma should also take the drug prophylactically".

He also proposed that the risk of side effects from low dose aspirin is far outweighed by the benefits.

Professor Sir Richard Doll agrees with him. Referring to the trial he told Medical Monitor: "I would prescribe aspirin for people at high risk of colorectal cancer. There is a very small risk of side effects such as bleeding from such low doses. And a small dose of aspirin is a good thing to take in preventing heart disease, too".