WASHINGTON, D.C.--A popular drug used to treat breast cancer also can prevent it in healthy older women with an elevated risk for the disease, according to results from a large clinical trial. "It's not often that we get to present results like these," said a jubilant National Cancer Institute director Rick Klausner, as he faced a bank of TV cameras at a press conference here today. But the drug--a synthetic estrogenlike compound called tamoxifen--has serious side effects, including risks of increasing endometrial cancer and blood clots among older women.
The $50 million study, conducted by a group of more than 300 clinics coordinated by the National Surgical Adjuvant Breast and Bowel Project (NSABP) in Pittsburgh, has shown that women with a high risk of getting breast cancer between the ages of 35 and 50 (or older women who have had a hysterectomy) are good candidates for taking this drug. The results were so strong, in fact, explains NSABP biostatistician Joseph Constantino, that the independent experts monitoring the data voted on 24 March to halt the study.
Preliminary analysis of the data show that the incidence of invasive breast cancers among tamoxifen users compared to the placebo group was reduced on average by 45%. In addition, the tamoxifen group had a lower rate of bone fractures. The risk of getting endometrial cancer turned out to be more than twice as high among tamoxifen users as among those on placebo. And the risk of developing a blood clot of the lung was three times higher in the tamoxifen group; two women in this group actually died of embolisms. But none of these increased risks were evident among women who began taking tamoxifen when they were under age 50.
Right now, researchers have only a sketchy idea of the risk from taking tamoxifen for the first time after age 50 (a time in life when cancer risk rises sharply) or using it for more than 5 years. For every patient, the potential benefits and risks must be balanced carefully--taking into account age and many personal factors--before a doctor can offer a recommendation for or against tamoxifen, said Klausner. The Food and Drug Administration hopes to give its recommendation on using tamoxifen as a preventive drug within 6 months.