Cost-effectiveness of zoledronic acid (ZOL) in postmenopausal women with early breast cancer receiving adjuvant letrozole.

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553 Background: In the ZO-FAST trial, postmenopausal women with early breast cancer and a bone mineral density (BMD) T-score ≥ –2 and receiving adjuvant letrozole (2.5 mg/day) were randomized to either immediate ZOL (4 mg/6 months) treatment (upfront ZOL) or to the same therapy but only when BMD T-score decreased to < –2 or fracture occurrence (delayed ZOL). After 60 months, upfront ZOL increased both BMD and disease-free survival (P < .05) relative to delayed ZOL. The present analysis assessed, from a US payer perspective, the cost effectiveness of upfront ZOL vs delayed ZOL in this population. Methods: A Markov state-transition model was developed to estimate the lifetime costs and quality-adjusted life-years (QALYs) for a hypothetical cohort of postmenopausal women with early breast cancer receiving letrozole with upfront or delayed ZOL. Consistent with ZO-FAST, patients were 57 years of age and breast cancer recurrence-free at baseline. Patients could progress over time to Local Recurrence, Contra-lateral Tumor, Distant Recurrence, or Death. Transition probabilities were derived from ZO-FAST, supplemented with literature. Costs and utilities were literature based. All outcomes were discounted 3% per year. Results: Compared to delayed ZOL, upfront ZOL resulted in better overall survival, disease-free survival, and QALYs, but at a higher cost (Table). In the base case, the incremental cost/QALY gained with upfront vs delayed ZOL was $7,967. In > 95% of 1,000 probabilistic sensitivity analysis runs, upfront ZOL costs less than $38,376/QALY gained. Conclusions: Upfront ZOL may increase survival and QALY and, at a cost per QALY well under the $50,000/QALY threshold, is very cost-effective in this population. [Table: see text]