BACKGROUND:In Breast International Group (BIG) 1-98, a randomized, double-blind trial comparing 5 years of initial adjuvant therapy with letrozole versus tamoxifen in postmenopausal women with hormone receptor-positive early breast cancer, letrozole significantly improved disease-free survival by 19% and reduced risk of breast cancer recurrence by 28% and distant recurrence by 27%.PATIENTS AND METHODS:A Markov model was used to estimate the incremental cost per quality-adjusted life year (QALY) gained with 5 years of initial adjuvant therapy with letrozole versus tamoxifen from a US health care system perspective. Probabilities and costs of breast cancer recurrence and treatment-related adverse events and health-state utilities were based on published results of BIG 1-98 and other published studies. Costs and QALYs were estimated over the lifetime of a cohort of postmenopausal women with hormone receptor-positive early breast cancer, aged 60 years at initiation of therapy. In our base case, we assumed that benefits of letrozole on risk of breast cancer recurrence are maintained for 5 years after therapy discontinuation ("carry-over effect") and examined the effects of this assumption on results in sensitivity analyses.RESULTS:Under base-case assumptions, letrozole yields an additional 0.409 QALYs versus tamoxifen at an additional cost of $9705, yielding a cost per QALY gained for letrozole versus tamoxifen of $23,743 (95% confidence interval, $14,087-$51,129). Assuming no carry-over effects, letrozole yields 0.264 QALYs at a cost of $10,341, for a cost per QALY gained of $39,098 (95% confidence interval, $23,968- $83,501).CONCLUSION:In postmenopausal women with hormone receptor-positive early breast cancer, initial adjuvant treatment with letrozole is cost-effective from the US health care system perspective.