BACKGROUND:In premenopausal women treated for breast cancer, loss of bone mineral density (BMD) follows from menopause induced by chemotherapy or loss of ovarian function biochemically or by surgical oophorectomy. The impact on BMD of surgical oophorectomy plus tamoxifen therapy has not been described. METHODS:In 270 Filipino and Vietnamese premenopausal patients participating in a clinical trial assessing the impact of the timing in the menstrual cycle of adjuvant surgical oophorectomy on breast cancer outcomes, BMD was measured at the lumbar spine and femoral neck before this treatment, and at 6, 12, and 24 months after surgical and tamoxifen therapies. RESULTS:In women with a pretreatment BMD assessment and at least 1 other subsequent BMD assessment, no significant change in femoral neck BMD was observed over the 2-year period (-0.006 g/cm2 , -0.8%, P = .19), whereas in the lumbar spine, BMD fell by 0.045 g/cm2 (4.7%) in the first 12 months (P < .0001) and then began to stabilize. CONCLUSIONS:Surgically induced menopause with tamoxifen treatment is associated with loss of BMD at a rate that lessens over 2 years in the lumbar spine and no significant change of BMD in the femoral neck.