A drug that cuts the risk that breast cancer patients will suffer a relapse may also prevent development of the disease in the first place, a study of mice showed Tuesday.

The study adds to the growing evidence that the drug tamoxifen may reduce the incidence of breast cancer, especially among women at high risk for the disease for reasons like family history of the disease.Tamoxifen is given routinely to some breast cancer patients after surgery and chemotherapy to reduce their risk of having a recurrence. The drug blocks the hormone estrogen, which some breast cancer cells need to grow.

But evidence has been mounting that the drug may be effective for preventing the cancer from developing in the first place.

In the new study, V. Craig Jordan and colleagues at the University of Wisconsin in Madison found tamoxifen sharply reduced the development of breast cancer in mice that received the drug for six months.

"The concepts illustrated in the present study may provide additional support for the use of tamoxifen as a chemopreventive agent in breast cancer," the researchers wrote.