Tamoxifen is one of the most widely prescribed drugs used to prevent the recurrence of breast cancer. A nonsteroidal antiestrogen, it has been successful in treating postmenopausal women at nearly all stages of breast cancer. Despite its popularity, disturbing questions remain about the use of this drug. How effective is tamoxifen in treating patients who have hormone-insensitive breast tumors or who have not yet reached menopause? What are the potential risks in taking tamoxifen, and do they ever outweigh its benefits? Should tamoxifen be administered as a prophylactic drug for healthy...