The headquarters of Swiss pharmaceutical company Novartis in Basel, Switzerland, are seen in this file picture taken Aug. 12, 2006.[Agencies]

A drug to prevent bone loss during breast cancer treatment also substantially cut the risk that the cancer would return, results that left doctors excited about a possible new way to fight the disease.

It is the first large study to affirm wider anti-cancer hopes for Zometa and other bone-building drugs called bisphosphonates. Zometa, made by Novartis AG, is used now for cancers that have already spread to the bone.

The new study involved 1,800 premenopausal women taking hormone treatments for early-stage breast cancer. Zometa cut by one-third the chances that cancer would recur — in their bones or anywhere else.

"This is an important finding. It may well change practice," said Dr. Claudine Isaacs, director of the clinical breast cancer program at Georgetown University's Lombardi Cancer Center.

About three-fourths of breast cancers occur in women after menopause. Zometa may help them, too, but it hasn't been tested yet in that age group.

The study was led by Dr. Michael Gnant of the Medical University of Vienna and reported Saturday at an American Society of Clinical Oncology conference in Chicago.

If a second, ongoing study also finds a benefit, doctors predict that Zometa will quickly be tested against other cancers that tend to spread, or metastasize, to bones, such as prostate and kidney cancer.