January 28, 2005 - Postmenopausal women treated with the breast cancer drug Femara® (letrozole) following surgery have a lower chance of relapse than women treated with tamoxifen, according to a new study.

Currently, tamoxifen is the standard treatment for postmenopausal women with early breast cancer. But the study, presented at the Primary Therapy of Early Breast Cancer 9th International Conference in Switzerland, showed that women had a 19% reduction in the risk of relapse if they used Femara. What's more, women who used Femara showed a 27% reduction in metastases, which is the spread of cancer to other sites in the body.

Femara is the second drug in a relatively new class of medications called aromatase inhibitors. These drugs work by blocking a substance called aromatase, whose normal function in post-menopausal women is to turn androgen hormones into estrogen. Blocking aromatase, in turn, lowers estrogen levels in the body, inhibiting the growth of some types of breast cancer. In contrast, tamoxifen blocks estrogen receptors on breast cancer cells, intercepting the hormone's ability to signal a tumour to grow faster.

In Canada, an estimated 21,200 women are diagnosed with breast cancer annually, and 5,200 will die from it. But the good news is that mortality rates from breast cancer are at their lowest since 1950, making finding a way for survivors to stay cancer-free a top priority.

The Femara study, which was funded by the drug's maker, Novartis, involved more than 8,000 postmenopausal women with early breast cancer from 27 countries around the world.

In particular, Femara was shown to be effective for women who are considered to be at high risk for relapse, either because their cancer had already spread to the lymph nodes before they were diagnosed or because they had previously received chemotherapy. Effects of Femara included an increased risk for osteoporosis and bone fracture, as well as higher rates of high blood cholesterol and occurrence of heart attacks and strokes than among the women using tamoxifen. But the women on tamoxifen were more likely to experience hot flashes, vaginal bleeding and endometrial cancer.

Femara is already approved in Canada for breast cancer patients who have been treated for 5 years with tamoxifen or who have more advanced breast cancer. But the study could help give aromatase inhibitors leverage to become more commonly used as an early treatment option.

In fact, a group of experts involved in a study funded by AstraZeneca, which makes a competing aromatase inhibitor drug called anastrozole (ARIMIDEX®), is calling for a panel of international experts to name ARIMIDEX® the "preferred breast cancer treatment option," after a study published in the Journal of Clinical Oncology said tamoxifen is no longer the best treatment for postmenopausal women with early breast cancer.

The study goes on to recommend that women who fit this category be treated with an aromatase inhibitor either initially or following treatment with tamoxifen.