Immediate Administration of Zoledronic Acid Reduces Aromatase Inhibitor-Associated Bone Loss in Postmenopausal Women With Early Breast Cancer: 12-month analysis of the E-ZO-FAST trial.

BACKGROUND: Letrozole is a proven and effective adjuvant therapy in postmenopausal women with hormone receptor-positive (HR(+)) early breast cancer (EBC). As with other aromatase inhibitors (AIs), long-term letrozole administration is associated with decreased bone mineral density (BMD) and increased fracture risk. This study compared potential bone-protecting effects of immediate vs. delayed administration of zoledronic acid (ZOL) in patients with EBC receiving adjuvant letrozole. PATIENTS AND METHODS: Patients with HR(+) EBC in whom adjuvant letrozole treatment was initiated (2.5 mg/day for 5 years) were randomized to immediate ZOL treatment (immediate ZOL) or delayed ZOL treatment (delayed ZOL) (both at 4 mg every 6 months). Patients in the delayed ZOL group received ZOL only for a BMD T-score that decreased to < -2.0 (lumbar spine [LS] or total hip [TH]) or for fracture. The primary endpoint was percentage change in the LS BMD at month 12. Patients were stratified by established or recent postmenopausal status, baseline T-scores, and adjuvant chemotherapy history. RESULTS: At 12 months, the LS BMD increased in the immediate ZOL group (+2.72%) but decreased in the delayed ZOL group (-2.71%); the absolute difference between groups was significant (5.43%; P < .0001). Across all subgroups, patients receiving immediate ZOL had significantly increased LS and TH BMD vs. those who received delayed ZOL (P < .0001). Differences in fracture incidence or disease recurrence could not be ascertained because of early data cutoff and low incidence of events. Adverse events were generally mild, transient, and consistent with the known safety profiles of both agents. CONCLUSION: Immediate ZOL administration effectively prevented BMD loss and increased BMD in postmenopausal women with HR(+) EBC receiving adjuvant letrozole, regardless of BMD status at baseline.