OBJECTIVES: The MA17 trial showed that addition of letrozole after 5 years tamoxifen was effective in further reducing the risk of relapse in women with breast cancer. Recent data also indicate that the cost of breast cancer relapse is much higher than previously shown, which has important implications for the benefit of adjuvant treatment. Further, the cost-effectiveness of adjuvant treatment from a societal perspective and in the Nordic countries is so far not extensively assessed.The objective of this study was to assess cost-effectiveness of extending the adjuvant therapy in Sweden, from a societal perspective. METHODS: Consequences for a woman at the age of 62 years who have completed 5 years tamoxifen treatment were assessed, from a societal and health care perspective. Clinical data on risk of relapse and adverse events were based on the MA17 trial. Costs, health utilities and survival data were based on recent detailed Swedish data. A reduction in relapse risk was extrapolated into a survival benefit, by assuming a higher mortality for patients with relapse. RESULTS: The total societal cost for letrozole- and placebo-treated patients were €7700 and €6300, respectively, a difference of €1500. The difference in life-years and QALYs were 0.23 and 0.18, respectively, leading to costs of €6500 per life-years gained and €8300 per QALY gained. The corresponding cost-effectiveness ratios from a health care perspective were €10,500 per life-years gained and €13,400 per QALY gained.CONCLUSIONS: The study indicates that the incremental cost per QALY gained for extended letrozole treatment in Sweden is low, and hence indicates that money spent of extending the adjuvant treatment with letrozole probably is money well spent in Sweden. More long-term data on the overall survival gain would be valuable to further validate the assumption used in the analysis.