Changing the way women are treated for breast cancer could improve their overall chance of survival, according to research published in the Lancet. The new paper shows that switching to a drug called exemestane, two to three years after commencing standard therapy with the drug tamoxifen, can cut the risk of death for certain women by a further 17% compared with using tamoxifen alone.

Postmenopausal women with early-stage hormone-sensitive primary breast cancer are usually treated with tamoxifen for five years, once they are free of disease, to reduce the risk of their cancer recurring. This therapy was once viewed as the 'gold-standard' treatment and it has been shown to cut the risk of death by 34%.

Over recent years, increasing numbers of these women have been receiving treatment with tamoxifen followed by Aromatase Inhibitors such as exemestane.

The Intergroup Exemestane Study (IES), which involved women from 37 different countries, has been examining the benefits of taking tamoxifen for two to three years and then switching to exemestane for the remainder of the five-year period. This new research is the first to show that early benefits of the tamoxifen and exemestane treatment sequence are maintained after treatment has stopped. The study, which was led by researchers from Imperial College London and The Institute of Cancer Research, was funded by Cancer Research UK and Pfizer.

The majority of breast cancer cases are hormone-sensitive, meaning that the cancer cells respond to estrogen and die when they are deprived of the hormone. Tamoxifen works by preventing estrogen from acting on cancer cells, whereas exemestane is an Aromatase Inhibitor, which works by stopping the body's production of estrogen.