Postmenopausal women who are at increased risk for developing invasive breast cancer may be eligible to participate. Candidates are screened with breast cancer risk assessment, medical history and physical examination, blood tests, review of medical records, if needed, breast biopsy, and dual energy x-ray absorptiometry (DEXA) scan to assess bone density. For the DEXA scan, the subject lies still on a table for about 30 minutes while the spine and hip are scanned using a small amount of radiation.