Upfront zoledronic acid significantly and progressively increases bone mineral density (BMD) in postmenopausal women with early breast cancer receiving letrozole for 5 years, according to results of the Zoledronic Acid–Letrozole Adjuvant Synergy Trial (Z-FAST).
This finding did not hold true if the zoledronic acid use was delayed (if a postbaseline lumbar spine or total hip T score decreased to less than -2.0, any clinical nontraumatic fracture occurred, or an asymptomatic vertebral fracture was identified at the 36-month follow-up). Patients in the delayed zoledronic acid group who were treated with zoledronic acid after bone loss had occurred did benefit by subsequent increases in BMD. Coadministration of zoledronic acid and letrozole was found to be well tolerated over 5 years, with fracture and disease recurrence rates similar in both groups.