Cost-effectiveness of subcutaneous versus intravenous trastuzumab for HER2-positive breast cancer in China: a partitioned survival model analysis

Given the established non-inferiority and comparable efficacy of subcutaneous (SC) and intravenous (IV) trastuzumab, this study aimed to explore the long-term economic implications of administration-route selection in the treatment of HER2-positive breast cancer from the perspective of the Chinese healthcare system. A partitioned survival model was developed using efficacy data from the HannaH phase III trial. Survival outcomes were extrapolated using curve-specific parametric models selected according to statistical fit and clinical plausibility. Trastuzumab acquisition and administration costs were applied only during the planned 18-cycle treatment period, whereas follow-up and disease-management costs were accumulated over a 20-year model horizon according to health-state occupancy. Costs were estimated in Chinese yuan from the Chinese healthcare system perspective and converted to 2025 US dollars using an annual average exchange rate of USD 1 = CNY 7.1429. The base-case discount rate was 4.5%, and the willingness-to-pay threshold was CNY 99,665/QALY, equivalent to USD 13,953/QALY. One-way sensitivity analysis, probabilistic sensitivity analysis, and scenario analyses were conducted to assess model uncertainty. The model projected nearly identical health outcomes for SC and IV trastuzumab. SC trastuzumab yielded 8.093 quality-adjusted life-years (QALYs) and 10.468 life-years (LYs), compared with 8.088 QALYs and 10.400 LYs for IV trastuzumab. The small incremental differences of 0.005 QALYs and 0.068 LYs arose from arm-specific survival extrapolation and should not be interpreted as evidence of clinical superiority. In the deterministic base-case analysis, total discounted costs were USD 85,219 for SC trastuzumab and USD 85,438 for IV trastuzumab, a difference of USD 219 in favour of SC trastuzumab. The corresponding incremental net monetary benefit was USD 288 at the specified willingness-to-pay threshold. Scenario analyses showed that the economic results were sensitive to survival extrapolation, IV biosimilar pricing, vial-sharing assumptions, discount rates, the model time horizon, and body-weight assumptions. The probabilistic sensitivity analysis showed no clear economic advantage. At the specified willingness-to-pay threshold, the probability that SC trastuzumab was cost-effective was 50.2%, whereas the probability that total costs were lower for SC than for IV trastuzumab was 49.8%. In this exploratory long-term economic evaluation, SC and IV trastuzumab produced comparable model-projected health outcomes. The deterministic analysis showed a small cost difference in favour of SC trastuzumab; however, the probabilistic analysis showed no clear economic advantage, with the probabilities that SC trastuzumab was cost-effective and had lower total costs being 50.2% and 49.8%, respectively. The economic results were sensitive to survival extrapolation, formulation prices, vial-sharing practices, discounting, the model time horizon, and body-weight assumptions.