OBJECTIVES: The objective of this study is to evaluate cost-effectiveness of pertuzumab in combination with trastuzumab and docetaxel for HER2-positive metastatic breast cancer in Japan. The National Institute for Health and Care Excellence (NICE) in the UK did not recommend pertuzumab due to poorer cost-effectiveness. While the Ministry of Health and Welfare of Japan decided to cover pertuzumab by health insurance in 2013, its cost-effectiveness in Japan has not yet been reported. METHODS: Cost-effectiveness analysis was performed using a Markov model based on clinical data from a phase III randomized double-blind placebo-controlled international multicenter clinical trial (CLEOPATRA). Pertuzumab in combination with trastuzumab and docetaxel was compared with trastuzumab and docetaxel. The base case was assumed to be a 50 year-old woman with HER2-positive metastatic breast cancer. Transition probability of each state in the model was estimated on the basis of the CLEOPATRA. As utility scores of Japanese metastatic breast cancer patients were not available, data from the NICE STA submission report were used. Costs were estimated on the basis of Japanese medical fee. Since our analysis was from the perspective of healthcare payer, only direct medical costs were included. Outcomes were measured in quality-adjusted life years (QALYs), and incremental cost-effectiveness ratio (ICER) was calculated. Two percent annual discount rate was used both for costs and outcome. The model used a time horizon of 25 years. RESULTS: Additional pertuzumab in combination with trastuzumab and docetaxel can gain more QALY (on average 0.85 QALY) than trastuzumab and docetaxel therapy. ICER of pertuzumab compared with control estimated to be about JPY 17 million per QALY (around £ 90,000, £ 1 = JPY 190). CONCLUSIONS: Pertuzumab in combination with trastuzumab and docetaxel is not cost-effective in our analysis, when £ 50,000 or less is judged to be cost-effective as ICER.