Direct and indirect economic evaluation of upfront and sequential adjuvant treatment in postmenopausal women with breast cancer based on the BIG 1–98 trial

6594 Background: The monotherapy arms of the BIG 1–98 trial established the clinical superiority of upfront letrozole (LET) relative to tamoxifen alone (TAM) but direct comparison of sequential TAM-LET, LET-TAM and upfront LET did not establish a clinically superior strategy. We undertook an economic evaluation to identify an economically preferred strategy based on the relative cost-effectiveness (CE) of TAM, LET, TAM-LET, and LET-TAM in terms of cost per quality-adjusted life year gained (QALYG). Methods: A state-transition model was developed to calculate cumulative costs and QALYs over a 25yr horizon for hypothetical cohorts of postmenopausal women with HR+ breast cancer undergoing adjuvant hormonal treatment. As the sequential arms were not directly compared to TAM alone, it was not possible to directly compare all strategies. As such, the analysis conducted direct within-arm comparisons and an indirect between-arm comparison. DFS endpoints and relative DFS benefit were derived from the monotherapy and sequential arms of BIG 1–98. Adverse events were not included as these have not yet been reported. Sensitivity analyses were conducted for the key parameters and assumptions, including the baseline recurrence risk and the duration of carry-over benefit. Costs and utility weights were derived from the literature. The analysis took a Canadian direct payer perspective and drug costs were based on 2008 Canadian average wholesale prices. Costs and outcomes were discounted at 3%. Results: In the monotherapy arms LET had a CE of $16,650 relative to TAM. In the sequential arms LET-TAM had superior QALYGs and cost savings relative to LET and TAM-LET. In economic terms, LET-TAM dominated LET and TAM-LET. In the indirect comparison, LET-TAM dominated LET and TAM-LET and had superior QALYGs at increased cost relative to TAM for a CE of $178. Conclusions: Direct comparisons confirm the economic favourability of LET relative to TAM and establish the dominance of LET-TAM over LET and TAM-LET. These indirect comparisons support the strong economic favourability of LET-TAM relative to TAM in the indirect comparison. In the absence of superior clinical outcomes, economic evaluation is a useful in suggesting a preferred strategy. No significant financial relationships to disclose.

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