By Jill Stein

SAN ANTONIO (Reuters Health) - Letrozole is more effective than tamoxifen as an initial hormone therapy in postmenopausal women with hormone-sensitive, early breast cancer, researchers announced here at the 2008 San Antonio Breast Cancer Symposium.

Some breast cancers are sensitive and to estrogen, which stimulates the cancer's growth. Letrozole attacks these cancers by decreasing the production of estrogen. Tamoxifen, on the other hand, stops estrogen from binding to cancer cells.

The current results, from an analysis of the Breast International Group (BIG) 1-98 study, showed that women who received letrozole for 5 years after surgery had a 13 percent lower risk of death than women treated with tamoxifen for the same period.

These findings provide the first evidence that an "aromatase inhibitor" drug like letrozole can provide better survival than tamoxifen, said co-investigator Dr. Henning T. Mouridsen, professor of oncology at Copenhagen University, Denmark, who reported the results on behalf of the BIG 1-98 Collaborative and the International Breast Cancer Study Group.

Letrozole improves survival primarily by preventing breast cancer relapse or spread to other body sites (metastasis), Mouridsen said.

Their study included 8,010 postmenopausal women who had completed surgery for estrogen-sensitive breast cancer and who had no evidence of metastasis.

Patients were randomly assigned to receive tamoxifen only for 5 years; letrozole only for 5 years; tamoxifen for 2 years followed by letrozole for 3 years; or letrozole for 2 years followed by tamoxifen for 3 years.

An analysis of the 4,922 patients assigned to the letrozole or tamoxifen only arms of the trial showed that women receiving letrozole monotherapy had a 13 percent lower risk of death even if they had been initially treated with tamoxifen then switched to letrozole.

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