OBJECTIVES: Zolbetuximab, the first monoclonal antibody targeting Claudin 18.2, was approved for advanced gastric or gastroesophageal junction adenocarcinoma (G/GEJ) by Japan’s Ministry of Health, Labour and Welfare (MHLW). We evaluate the cost-effectiveness of adding zolbetuximab to chemotherapy (CAPOX or mFOLFOX) versus chemotherapy alone from Taiwan's National Health Insurance (NHI) perspective.

METHODS: Using efficacy data from GLOW and SPOTLIGHT trials, we employed two 3-state partitioned survival models to evaluate the cost and effectiveness of adding zolbetuximab to mFOLFOX or CAPOX over a 10-year horizon. A hypothesized price of zolbetuximab (NT$11,990 per 100 mg per m²) was assigned based on Japan’s MHLW, while chemotherapy and non-medication costs were derived from Taiwan’s NHI claim data. Other parameters were sourced from published literature. Incremental cost-effectiveness ratios (ICERs) were calculated and compared against the willingness-to-pay threshold (3 times the gross domestic product per capita in 2023, NT$3,023,055). Quality-adjusted life-years (QALYs) and costs were discounted at 3%. Scenario analyses explored the impact of varying zolbetuximab prices. Deterministic and probabilistic sensitivity analyses were conducted to assess uncertainty.

RESULTS: Based on the hypothesized price, adding zolbetuximab to CAPOX resulted in a 0.38 QALY gain at NT$1,109,392 incremental cost, with an ICER of NT$2,940,727 per QALY and a 55.7% probability of cost-effectiveness. Conversely, adding zolbetuximab to mFOLFOX yielded 0.42 QALY gains at NT$1,705,641 incremental cost, with an ICER of NT$4,024,348 per QALY and a 26.7% probability of cost-effectiveness. A 50% price reduction improved mFOLFOX's ICER to NT$2,938,369 per QALY with a 56.6% probability of cost-effectiveness.

CONCLUSIONS: Adding zolbetuximab to CAPOX is cost-effective at the hypothesized price. However, for adding it to mFOLFOX to be cost-effective, a 50% price reduction is necessary.