These women started taking letrozole anywhere from one to seven years after they stopped taking tamoxifen.

NPR: Study: Drug Can Curb Breast Cancer Recurrence

And there are millions more in other countries who might benefit from letrozole.

NPR: Study: Drug Can Curb Breast Cancer Recurrence

Three aromatase inhibitors are set for tentative approval - anastrozole, exemestane and letrozole.

BBC: Earlier use of cancer drug backed

Over five years researchers compared them to 800 women who had taken placebos earlier and elected not to take letrozole.

NPR: Study: Drug Can Curb Breast Cancer Recurrence

There were two-thirds fewer breast cancer recurrences among women who took letrozole.

NPR: Study: Drug Can Curb Breast Cancer Recurrence

He says many American breast cancer patients are already taking letrozole after a five year course of tamoxifen because of the earlier study, but some aren't.

NPR: Study: Drug Can Curb Breast Cancer Recurrence

This time, researchers looked at 1, 600 women who had been on a placebo in the earlier study but decided to take letrozole after that was finished.

NPR: Study: Drug Can Curb Breast Cancer Recurrence

Half of them didn't start letrozole for about three years.

NPR: Study: Drug Can Curb Breast Cancer Recurrence

It showed that breast cancer patients who took tamoxifen for five years and then switched to another estrogen blocker called letrozole had a much lower risk the cancer would come back.

NPR: Study: Drug Can Curb Breast Cancer Recurrence

Dr. WEINER: Around the world there are certainly many women who have been on tamoxifen for five years, have been off all therapy for a few years, and might consider going on a drug like letrozole or specifically letrozole based on these results.

NPR: Study: Drug Can Curb Breast Cancer Recurrence