OBJECTIVES: To develop an evidence-based clinical and economic decision-analysis model to identify existing treatment patterns and estimate the costs and outcomes for early, recurrent, and metastatic breast cancer in Japan. METHODS: Treatment patterns and probability distributions for the Japanese Breast Cancer Treatment Model (JBCTM) were identified and confirmed via a series of meetings with a clinical expert panel and a study-specific survey of practice patterns of over 500 Japanese breast cancer physicians. Since no Japanese guidelines for evaluating level-of-evidence data yet exist, guidelines from the American Society of Clinical Oncology were used to stratify the clinical usage and clinical outcomes data for every drug. Consideration was given to disease stage and treatment setting in assigning the level of evidence, and nodal status, hormone receptor status, and menopausal status were also considered. Costs were obtained from government sources and hospital provider surveys and validated by an expert panel. RESULTS: The model features treatment pathways for four breast cancer stages and resources and costs for every treatment option in the model. In total, the model includes over 450 level-of-evidence references for more than 60 drug treatments. The model can generate responses to an infinite number of queries regarding the probabilities of receiving a particular treatment in a given setting, cost per treatment, expected cost per patient, and an estimate of cost-effectiveness with consideration given to the evidence level associated with treatments. CONCLUSIONS: To incorporate level-of-evidence data into a comprehensive treatment model, level-of-evidence guidelines can be applied to treatments in a given setting and combined with published data, data from surveys, and expert opinion to generate a valuable decision-making tool. The treatment pathways, costs and cost-effectiveness, and the evidence level associated with those pathways can then be evaluated on the credibility of clinical results.