Aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) have been found to be associated with a reduced risk of developing breast cancer. In a study published in the Journal of the American Medical Association (JAMA) women who regularly took aspirin for pain relief were found to have a 20 percent lower risk than women who did not take the painkiller. Aspirin is also thought to help protect against other cancers, for example of the bowel and colon.

However, the current recommendations are that women should not start to take aspirin to help prevent breast cancer because the painkiller is associated with other, unwanted, side-effects such as gastrointestinal problems.

Below we look at the issue in more depth:

By how much did aspirin and NSAIDs reduce the risk of developing breast cancer?

Women who had taken aspirin at least once a week for six months had a 20 percent lower risk of developing breast cancer.

Women who took at least seven aspirin tablets a week (the equivalent of at least one a day) had their risk of breast cancer reduced by 28 per cent.

Women who took NSAIDs also reduced their risk of developing breast cancer, but the effect was not as great as it was for aspirin.

Women who took painkillers that were not aspirin or NSAIDs did not have a reduced risk of developing breast cancer.

Should women take aspirin regularly to reduce their risk of breast cancer?

No. The benefits of taking aspirin and NSAIDs regularly need to be balanced against the risks of long-term use: for example long-term aspirin use has been found to cause stomach ulcers and bleeding of the stomach lining. For this reason, until more research has been carried out, aspirin and NSAIDs cannot be recommended as a long-term preventive treatment for breast cancer.

Does aspirin help to protect against all forms of breast cancer?

No. Aspirin and NSAIDs appear to only help to protect against breast cancers that are stimulated by oestrogen. These “hormone receptor-positive” cancers are the most common form of breast cancer.

However, because of the way that aspirin and NSAIDs work, they have no effect on hormone receptor-negative cancers.

Why is it that aspirin only has an effect on hormone receptor-positive cancers?

Hormone receptor-positive breast cancers are affected by the levels of oestrogen and progesterone present in breast tissue. The higher the levels of these hormones, the more the cancer cells are stimulated to grow and divide. Aspirin and NSAIDs help to reduce the risk of hormone receptor-positive breast cancer by reducing the levels of oestrogen.

Aspirin and NSAIDs reduce the amount of oestrogen in breast tissue by acting on a mechanism that controls oestrogen production. The final step in the production of oestrogen is controlled by a catalyst called aromatase cytochrome P450 and the amount of catalyst is controlled by prostaglandins. While the amount of prostaglandins is controlled by an enzyme called cyclooxygenase (COX) and this enzyme is affected by aspirin and NSAIDs. Aspirin and NSAIDs prevent COX from making prostaglandins, which in turn reduces the amount of aromatase produced, which in turn reduces the amount of oestrogen produced.

How was the study carried out?

The study was carried out by researchers at the University of Columbia who looked looked at 1442 women with breast cancer and 1420 women without breast cancer. The women were asked about their use of aspirin, non-steroidal anti-inflammatory drugs (NSAIDs) and non-NSAID painkiller paracetamol. The results of the study were published in the 26 May 2004 issue of the Journal of the American Medical Association (JAMA 2004: 291; 2433-2440).