The Food and Drug Administration approved a drug that has been shown to sharply reduce the risk of breast-cancer recurrence for use in postmenopausal women after five years of standard cancer treatment with Tamoxifen.

The approved drug, Femara, made by Swiss drug company Novartis AG is already on the U.S. market for use in women with advanced breast cancer that has spread to other parts of the body.

Femara's new indication, however, marks the first time that a drug has been approved as a treatment beyond Tamoxifen, which is made by British drug company AstraZeneca PLC and is also available as a generic.

"It's a massive advance" in breast-cancer treatment, said Paul Goss, the chief investigator for the Femara clinical trial, known as MA-17. Dr. Goss heads Massachusetts General Hospital's breast cancer division and is also a Harvard University professor.

Dr. Goss's study of 5,200 postmenopausal women showed that Femara reduced the risk of breast-cancer recurrence by more than 40% in women taking Femara after an average of 2.5 years, compared with women on a placebo, or a sugar pill. The results of the clinical trial were so successful that women on the placebo were offered the chance to go on Femara. The FDA granted Femara fast-track priority review status.

Dr. Goss said that Tamoxifen is very effective at treating breast cancer but that it appears to lose its effectiveness after five years and might increase the risk for other types of cancer.

After the five-year mark, most women are then just monitored for any recurrence of cancer. Now, Dr. Goss said, patients can be put on Femara, which is significant because two-thirds of breast cancer recurrences and deaths happen more than five years after the initial diagnosis, or post-Tamoxifen.

About 100,000 women complete Tamoxifen therapy each year in the U.S. American women have about a one in eight chance of being diagnosed with breast cancer. About 200,000 new cases are diagnosed each year.

David R. Epstein, president of Novartis Oncology, said the company would immediately begin marketing of Femara, a pill taken once daily, for use in women after they have stopped taking Tamoxifen.