by James J. Galligan, Ph.D., Associate Chair,baby aspirin image
Department of Pharmacology and Toxicology

We are always looking for better drugs to treat diseases. Pharmaceutical companies invest billions of dollars in research and development to understand disease mechanisms so that new targets for drug treatments can be identified. Cancer of all kinds is a disease that everyone fears and fortunately there has been great progress in diagnosing and treating cancer. With a few exceptions, cancer is not the death sentence it was at one time.

Perhaps even better than treating an existing cancer, is preventing cancer in the first place. This is where a recent study by Rothwell and colleagues comes in. Their study published in the Lancet shows that daily, low doses of aspirin reduce the risk of developing colon cancer.

It has been known for many years that a baby aspirin taken daily (about 80 mg of aspirin) reduces the risk of heart attack and stroke. This is because aspirin reduces blood clots which can block the small blood vessels that supply the heart and brain.

Aspirin inhibits an enzyme called cyclooxygenase 1 (COX-1) in blood platelets. COX-1 synthesizes factors that cause platelets to clump (aggregate) and clumping platelets form blood clots. Aspirin also inhibits a related enzyme called COX-2. COX-2 accumulates at sites of tissue injury and inflammation. COX-2 is also found in pre-cancerous tissues in the colon called adenomas. COX-2 activity helps to transform adenomas into cancer cells. By inhibiting COX-2 lowly aspirin can help prevent colon cancer.

Rothwell and colleagues analyzed data from five different placebo-controlled studies of the effects of aspirin on the incidence of heart and stroke. They looked at the occurrence of colon cancer in the study participants and found that aspirin produced a substantial decrease in colon cancer rates.

There are a couple of important additional findings. Firstly, there was a modest dose-related effect. Aspirin doses of 30 mg per day or less had no effect on colon cancer rates while doses higher than 80 mg per day were no better than a dose of 80 mg. The reason this is important is because a major side effect of aspirin therapy is gastrointestinal bleeding. The risk of gastrointestinal bleeding increases with daily aspirin doses more than 80 mg per day. The risk of gastrointestinal bleeding with a daily aspirin dose of 80 mg is small but not zero. Anyone considering daily low doses of aspirin for reducing the risk of heart attack, stroke or colon cancer needs to consult with their doctor first.

Aspirin has been around for more than 100 years. It is inexpensive and if used properly it can help prevent some of the biggest killer diseases. Sometimes the answer is right there in front of us and in the case of colon cancer, aspirin has been sitting there quite awhile.