The effect of tamoxifen or exemestane on bone mineral density during the first 2 years of adjuvant treatment of postmenopausal women with early breast cancer

BACKGROUND: Adjuvant therapy with aromatase inhibitors is associated with increased bone loss in postmenopausal women with breast cancer. We assessed changes in bone mineral density (BMD) from baseline to 24 months in patients receiving either tamoxifen (T) or exemestane (E). PATIENTS AND METHODS: A total of 578 women randomly assigned to T 20 mg per day orally or E 25 mg/day orally enrolled in this substudy; baseline, 12-month, and 24-month BMD measurements of the femur and lumbar spine by dual-energy x-ray absorptiometry were planned. Women receiving bone antiresorptive agents were excluded. Mean BMD changes from baseline to 12 and 24 months were tested between the treatment groups using 2-sample t tests and both g/cm2 (as percent changes) and T scores (as differences from baseline). RESULTS: A total of 167 women with all 3 imaging studies were evaluable and form the basis of this report (T=89, E=78). Using T scores, the mean difference from baseline was significant between the 2 groups at 12 months at both the spine (P=.0002) and the hip (P=.0004), and at 24 months only at the hip (P=.02). CONCLUSION: More bone loss occurred during the first 12 months of treatment with E compared with T, but by 2 years the differences were less apparent and bone loss with E had slowed.