Aromatase inhibitors (AIs) are accepted as adjuvant therapy for postmenopausal women (PMW) with hormone-responsive early breast cancer (EBC) with superior efficacy to tamoxifen. However, increased bone loss is associated with AIs.

PMW with EBC receiving letrozole (2.5 mg/day for 5 years) were randomly assigned to immediate zoledronic acid (ZOL; 4 mg every 6 months) or delayed ZOL (initiated only for fracture or high risk thereof).

Patients (N = 1065) had a median age of 58 years; 54% had received prior adjuvant chemotherapy. At 36 months, mean change in L2-L4 bone mineral density (BMD) was +4.39% for immediate versus -4.9% for delayed ZOL (P < 0.0001). Between-group differences were 5.27% at 12 months, 7.94% at 24 months, and 9.29% at 36 months (P < 0.0001 for all). At 36 months, the immediate-ZOL group had a significant 41% relative risk reduction for disease-free survival (DFS) events (P = 0.0314). Adverse events are consistent with the known safety profiles of the study drugs.

At 36 months, immediate ZOL was more effective in preserving BMD during letrozole therapy. Immediate versus delayed ZOL led to significantly improved DFS. Benefits are observed in the context of a favorable, well-established safety profile for letrozole and ZOL.

PMID: 20444845 [PubMed - as supplied by publisher] Source: National Library of Medicine.