€OBJECTIVES: To obtain a Dutch cost-effectiveness estimate of trastuzumab in early breast cancer, based on a previous UK model-based cost-effectiveness analysis. Trastuzumab is a humanized monoclonal antibody against the HER2-receptor extracellular domain. METHODS: Following the model transferability assessment, required adjustments were made. In a Markov cohort model, 1 year adjuvant trastuzumab therapy was compared to observation. Model outcomes are life years, quality-adjusted life years (QALYs),  healthcare costs, and cost of productivity loss. The cycle length is one year, the time horizon is lifetime. UK prices were replaced by updated Dutch unit prices. Clinical input data originated from the HERA-trial; health utilities were obtained from literature. The impact of parameter uncertainty was assessed using age subgroup analyses, one-way sensitivity analyses and probabilistic sensitivity analysis. Subsequently, we conducted expected value of perfect information analyses. RESULTS: In the Netherlands, from a health care perspective the ICER for trastuzumab for a 55 year old patient was estimated at €19,463/QALY. From a societal perspective the ICER became €14,867. As expected, ICERs improve with younger age. Sensitivity analyses showed that the ICER was sensitive to the time horizon and the costs for the metastasic health state. CONCLUSIONS: Overall the Dutch cost-effectiveness estimate of trastuzumab for early stage breast cancer can be well described and is well below the Dutch informal threshold of  €80,000/QALY. For the base case analysis the probability that the ICER is acceptable for thresholds above €27.000/QALY is 1, indicating a probability of zero for a wrong decision. Hence, for thresholds above €27,000 the expected value of information is zero. This analysis provided an early cost-effectiveness indication of  trastuzumab  in the adjuvant setting in the Netherlands and has led to the provisional reimbursement. The transferability assessment is addressed in a separate abstract.