Postmenopausal women with the most common type of metastatic breast cancer now have a new treatment option that lengthens their lives, according a study led by UC Irvine oncologist Dr. Rita Mehta and conducted by the Southwest Oncology Group. The findings appear in the Aug. 2 issue of the New England Journal of Medicine.

A combination of the two anti-estrogen drugs anastrozole and fulvestrant extended the median survival time of women with Stage 4 hormone receptor-positive metastatic breast cancer by more than six months compared to those who underwent standard treatment with anastrozole alone.

Mehta said the results of the Phase 3 trial are particularly exciting because "these patients have not had a new treatment that gave them an overall survival benefit in more than a decade."

Both drugs are currently used to treat breast cancer, though not in combination. Anastrozole (also known as Arimidex) reduces the production of tumor-promoting estrogen, while fulvestrant (Faslodex) interferes with the receptors that allow estrogen to signal cells to grow and reproduce and also accelerates the degradation of these receptors.

The researchers think it's these modes of action together that make the combination so effective against hormone receptor-positive breast cancer, a subtype that accounts for more than half of all breast cancers.

"The next step would be to try the combination in even earlier stages of breast cancer to see whether long-term cures could be increased at those stages," said Mehta, an associate clinical professor of medicine with the Chao Family Comprehensive Cancer Center and an oncologist with UC Irvine's Breast Health Center.

Study results were first presented at the 2011 CTRC-AACR San Antonio Breast Cancer Symposium in December. The SWOG S0226 trial was conducted by the SWOG clinical trials network, previously known as the Southwest Oncology Group.