'A Big Deal,' But a Complex Hand to Play

A $50 million study sponsored by the National Cancer Institute has established unequivocally that a synthetic estrogen-like compound called tamoxifen was effective in reducing the incidence of breast cancer in a group of healthy women over age 35 with a higher than normal risk. But some key issues remain unsettled, such as whether women with the BRCA1 and BRCA2 genetic mutations might benefit from using tamoxifen, whether side effects increase with the duration of use, and when it is best to begin taking the drug.