Cost-Utility and Budget Impact Analysis of Biosimilar Trastuzumab for Early-Stage HER2- Positive Breast Cancer in Thailand: An Updated Evaluation Supporting Expanded Access

Background Trastuzumab is an established adjuvant therapy for early-stage HER2-positive breast cancer. Previous studies in Thailand demonstrated its cost-effectiveness, but earlier evaluations did not account for trastuzumab-related cardiac adverse events, costs of HER2 and hormone receptor testing, or the budgetary implications of expanding treatment eligibility. This updated economic evaluation incorporates biosimilar drug pricing, the clinical and economic burden of cardiotoxicity, and diagnostic testing costs, and assesses the impact of expanding access to patients with node-negative tumors larger than 2 cm and ER/PR-negative status. Methods A cost-utility analysis using a Markov model was conducted from a societal perspective over a lifetime horizon, comparing trastuzumab plus paclitaxel with paclitaxel monotherapy. Updated costs, transition probabilities for disease progression and cardiac events, and utility weights were applied. Direct medical, direct non-medical, and indirect costs were included, adjusted to 2024 Thai Baht (THB), with costs and quality-adjusted life years (QALYs) discounted at 3% annually. A budget impact analysis estimated the incremental cost of expanding reimbursement criteria to the additional eligible subgroup. Results 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 (ICER) of THB 83,520 per QALY gained, well below Thailand’s cost-effectiveness threshold of THB 160,000 per QALY. Incorporating cardiac toxicity and diagnostic testing costs had minimal impact on ICER, reflecting the low incidence and reversibility of cardiotoxicity. The projected annual budget impact of expanding coverage to the additional patient subgroup was THB 53.9 million, representing a modest increase relative to expected clinical benefits. Conclusions Biosimilar trastuzumab remains a cost-effective adjuvant therapy for early-stage HER2-positive breast cancer in Thailand, even after accounting for cardiac adverse events and diagnostic testing costs. The findings support expanding reimbursement to high-risk node-negative patients with ER/PR-negative tumors larger than 2 cm, consistent with value-based policy expansion and efficient use of healthcare resources.