Orlando, Fla. ? A new study gives encouraging signs that a hormonal drug used to fight breast cancer might help prevent abnormal prostate growths from turning into cancers.

Men who took low doses of the drug for a year cut their chances of developing prostate cancer roughly in half, doctors reported Saturday at meeting of the American Society of Clinical Oncology.

The findings need to be tested in larger studies, specialists say. But this is the first time any drug has been shown to prevent a precancerous condition from forming a tumor.

As many as 50,000 men each year are diagnosed with such growths, and then suffer constant worry and frequent biopsies to see whether cancer has developed.

The drug is toremifene, sold as Acapodene for treating advanced breast cancer. It selectively blocks some of the effects of estrogen, a hormone men have but in much smaller quantities than women.

For decades, prostate cancer prevention and treatment has focused on blocking the male hormone, testosterone. Targeting estrogen “opens up a new area,” said the cancer society’s medical director, Dr. Harmon Eyre.

Prostate cancer is the most common major cancer in the United States. More than 230,000 new cases and about 30,000 deaths from it are expected this year.

Men who have abnormal growths called prostatic intraepithelial neoplasia, or PIN, have about a 30 percent chance of developing prostate cancer within a year and about a 65 percent chance within two years.