The new drug exemestane for breast cancer treatment could improve survival rates by 17 percent, new research shows.

A study of 4,742 post-menopausal women found that switching from the present gold-standard breast cancer treatment tamoxifen to the new drug exemestane after two or three years resulted in a dramatic fall in death rates, The Times newspaper reported on Tuesday.

The new drug, sold under the brand name Aromasin, is recommended by the National Institute for Health and Clinical Excellence as an alternative to tamoxifen after two to three years, according to the report.

The study followed the progress of women treated for a total of five years and monitored for a further three years, and women assigned randomly to a full five years of tamoxifen, or treatment with tamoxifen followed by exemestane.

The researchers said that giving women tamoxifen after surgery already reduced the risk of dying by 33 percent, and after another two to three years of exemestane, and with a further three years of post-treatment follow-up, survival was found to be significantly improved with the risk of dying 50 percent lower than if they had received no drug therapy.

“This is the first time any hormone treatment has been shown to reduce the death rate more than tamoxifen alone. Switching drugs also seems to avoid the side-effects of long-term tamoxifen therapy, such as cancer of the womb and deep vein thrombosis,” Charles Coombes, director of the Cancer Research UK Laboratories and head of cancer medicine at Imperial College, London, was quoted as saying.

The charity Cancer Research UK, whose scientists were involved in the study, said that the treatment would prevent an estimated 1, 300 annual deaths in this country.