Aromatase inhibitors work by blocking the production of estrogen, which is known to play a key role in the development and growth of breast cancer.

Aromasin is a hormonal therapy that belongs to a class of drugs called aromatase inhibitors. They work by blocking the production of estrogen, which is known to play a key role in the development and growth of breast cancer.

For many years, treatment with tamoxifen has been the standard hormonal therapy for postmenopausal women with breast cancer that is dependent upon estrogen for growth.

Significant Increase in Disease-Free Survival

Results from the pivotal Intergroup Exemestane Study (IES), published in the New England Journal of Medicine, demonstrated that postmenopausal breast cancer patients who had been treated with 2-3 years of tamoxifen for early breast cancer (adjuvant treatment with tamoxifen) and were switched to Aromasin significantly reduced their risk of recurrence and increased disease-free survival compared to patients who remained on tamoxifen for the entire five years.

"The adjuvant approval of Aromasin would provide oncologists with a treatment regimen that significantly reduces the recurrence of breast cancer," said Dr. Stephen Jones, medical director at U.S. Oncology Research. "This filing is an important step toward providing postmenopausal women with a critical treatment option that can significantly improve survival of early breast cancer when compared to tamoxifen."

Fewer Cases of Contralateral Breast Cancer

Pfizer's announcement closely follows newly released American Society of Clinical Oncology (ASCO) recommendations on the use of aromatase inhibitors as adjuvant therapy for postmenopausal women with hormone-receptor-positive breast cancer and coincides with the presentation of an update on the study trial being used to support the filing.

The ASCO recommendations, published in the Journal of Clinical Oncology, included among its treatment options for women initially started on tamoxifen a switch to an aromatase inhibitor based on data from the Aromasin study, IES.

Professor Charles Coombes, Director of the Cancer Research UK Laboratories at Imperial College London, Hammersmith and Charing Cross Hospitals, presented an update from the IES Wednesday at the 27th Annual San Antonio Breast Cancer Symposium based on 37.4 months of median follow-up and 4,740 patients.

These findings showed that 193 women treated with exemestane experienced a local or distant recurrence of disease compared with 264 women who continued on tamoxifen. A 30 percent reduction in risk of recurrence in breast cancer was reported when women were switched to Aromasin after 2-3 years of tamoxifen, compared to those who continued on tamoxifen for a total of 5 years, the current standard of care (P=0.00005).

In addition, 54 percent fewer cases of contralateral breast cancer (12 vs. 26) developed in women treated with Aromasin compared to those who remained on tamoxifen (P=0.04).

Blocks Estrogen Production

Breast cancer is the second leading cause of cancer death among women. It is estimated that 213,910 women in the United States will be diagnosed with breast cancer in 2004 and more than 40,921 women will lose their lives to the disease. Breast cancer is estrogen-dependent in 2/3 of all cases.

Aromasin (exemestane) was approved in the United States late in 1999 for the treatment of advanced breast cancer in postmenopausal women whose tumors have stopped responding to tamoxifen. It also is approved for use in Europe, Japan and South America.

Unlike other aromatase inhibitors, exemestane is a steroidal aromatase inactivator, which means it selectively targets and irreversibly binds to the aromatase enzyme, which is required to produce estrogen. Without estrogen, breast cancer cells cannot survive.

Exemestane is well tolerated and the side effects associated with the treatment are generally predictable and manageable. Exemestane should not be administered to premenopausal women and women who are pregnant. Dose modifications should be considered for patients taking concomitant CYP3A4 inducers. The most common side effects for exemestane were mild to moderate and were associated with low-grade nausea (18%) and hot flashes (13%).