Economic Evaluation and Budget Impact of Biosimilar Trastuzumab for HER2-Positive Metastatic Breast Cancer in Thailand: Policy Implications for Access and Affordability

Objectives To evaluate the cost-utility and budget impact of biosimilar trastuzumab plus paclitaxel versus paclitaxel monotherapy for HER2-positive metastatic breast cancer in Thailand and to explore policy implications for access and affordability. Methods A Markov model was developed from a societal perspective over a lifetime horizon, simulating 3 health states: stable disease, progressive disease, and death, in 3-week cycles. Two trastuzumab-based strategies were evaluated: (1) fixed-duration treatment for 1 year and (2) continuous treatment until disease progression. All costs were updated to 2024 values using local data. Clinical effectiveness was measured in quality-adjusted life-years (QALYs). A probabilistic sensitivity analysis and a 5-year budget impact analysis were performed. Results Compared with paclitaxel monotherapy, trastuzumab plus paclitaxel increased life-years by 0.31 and QALYs by 0.27. The incremental cost-effectiveness ratios were Thai Baht (THB) 195 541/QALY for the 1-year regimen and THB 231 119/QALY for the continuous regimen, both exceeding Thailand’s cost-effectiveness threshold of THB 160 000/QALY. The 5-year budget impact was estimated at THB 166.3 million and THB 199.3 million, respectively. Price reductions would be required for trastuzumab to achieve cost-effectiveness under the Thai threshold. Conclusions Although biosimilar trastuzumab has improved affordability, it remains not cost-effective at current prices. However, the relatively modest budget impact supports the feasibility of expanding access through targeted price negotiation and policy interventions. Threshold analysis indicated that price reductions to approximately THB 3700 per vial (1-year regimen) and THB 2950 per vial (until-progression regimen) would be required for trastuzumab to achieve cost-effectiveness under the Thai threshold.