A reduction in breast density of at least 10 percent may predict who benefits from the breast cancer preventive effects of tamoxifen. Researchers studied 1,063 women and found that those with reduced breast density after 12 to 18 months of treatment had a 52 percent reduced risk of breast cancer. By contrast, those women who did not have a decrease in breast density had only an eight percent risk reduction. Jack Cuzick, Ph.D., at the 2008 San Antonio Breast Cancer Symposium