Evaluation of the protective effects of zoledronic acid on bone mass in premenopausal women undergoing adjuvant chemotherapy following treatment discontinuation
562 Background: Adjuvant chemotherapy is associated with a significant reduction in bone mineral density (BMD) in premenopausal women with breast cancer (BC). We previously showed that this loss of BMD can be prevented with zoledronic acid (ZA) every 3 months for a year. Since bone loss in women with osteoporosis is prevented with annual ZA, we examined whether protection from bone loss by ZA in women with BC persists following discontinuation of ZA. Methods: A randomized, double-blind, multicenter, phase III trial comparing ZA (4 mg every 3 months) versus placebo for 1 year in premenopausal women with BC undergoing adjuvant chemotherapy was conducted. Patients had serial BMD measurement at 0 (after surgery and before chemotherapy), 6, 12 and 24 months. Demographic, clinical, and tumor characteristics were collected. Serum was stored at -70°C and analyzed in batches. The secondary outcome of percent change in BMD at 24 months, one year following the last ZA/placebo, is presented. Intention-to-treat analyses with linear mixed models were performed using SAS version 9. Results: Of 101 patients randomized, 85 completed 12 month, and 62 completed 24 month evaluations; mean age 41 (SD 5.2). Demographic and baseline characteristics were similar between treatment groups. By 24 months, 38 (61%) had not regained their menses; 22 patients were on tamoxifen, 25 were on an aromatase inhibitor. Chemotherapy without ZA was associated with a significant decline from baseline in lumbar spine (LS) BMD after both 12 (-5.4%) and 24 (-6.3%) months. Similarly total hip (TH) and femoral neck (FN) BMD declined by 2.6% and 2.4% by 24 months, respectively. In contrast, BMD remained stable in ZA-treated patients (p < 0.0001 vs placebo). Patients who received ZA had stable BMD at 24 months (LS -0.58%, TH 0.83%, FN 0.04%). Analysis of bone turnover markers is ongoing. Conclusions: Premenopausal women receiving adjuvant chemotherapy for BC had significant bone loss in the first year that persisted in the second year. ZA every 3 months for a year effectively prevented bone loss during the first year and 1 year after completion of ZA treatment. One year of ZA maintains BMD in premenopausal BC patients for an additional year after discontinuation of ZA. [Table: see text]