Cost-utility and budget impact analysis of biosimilar trastuzumab for early-stage HER2-positive breast cancer in Thailand: an updated evaluation supporting expanded access

Trastuzumab is an established adjuvant therapy for early-stage HER2-positive breast cancer. Previous economic evaluations in Thailand demonstrated its cost-effectiveness; however, earlier analyses did not incorporate trastuzumab-associated cardiac toxicity, costs of HER2 and hormone receptor testing, or the budgetary implications of expanding reimbursement eligibility. This study aimed to provide an updated economic evaluation using current biosimilar pricing and to assess the affordability of expanded access under Thailand’s Universal Health Coverage scheme. A cost–utility analysis using a Markov cohort model was conducted from a societal perspective over a lifetime horizon, comparing adjuvant trastuzumab plus paclitaxel with paclitaxel monotherapy. The model incorporated disease progression, cardiac toxicity, and mortality. Costs and health outcomes were expressed in 2024 Thai Baht (THB), and quality-adjusted life years (QALYs) were discounted at 3% annually. A budget impact analysis was performed to estimate the fiscal implications of expanding reimbursement to high-risk node-negative patients. Trastuzumab plus paclitaxel resulted in higher lifetime costs (THB 989,794 vs. THB 606,142) and greater health benefits (12.69 vs. 8.10 QALYs) than paclitaxel alone, yielding an incremental cost-effectiveness ratio of THB 83,520 per QALY gained, which is well below Thailand’s cost-effectiveness threshold of THB 160,000 per QALY. Incorporating diagnostic testing and cardiac toxicity costs had minimal impact on cost-effectiveness results. The annual budget impact of expanding coverage was estimated at THB 53.9 million, reflecting a modest increase relative to the expected health gains. Using current biosimilar pricing, adjuvant trastuzumab remains a cost-effective intervention for early-stage HER2-positive breast cancer in Thailand. The findings support expanding reimbursement to selected high-risk node-negative patients, demonstrating that such policy expansion can deliver substantial health benefits while remaining affordable within existing healthcare budgets.