Cost-Effectiveness of Pembrolizumab Plus Trastuzumab and Chemotherapy Versus Trastuzumab Plus Chemotherapy as First-Line Treatment of HER2-Positive Gastric or Gastroesophageal Junction Adenocarcinoma in China.

OBJECTIVE: This study aimed to evaluate the cost-effectiveness of pembrolizumab in combination with trastuzumab and chemotherapy (PEM + TRAS + Chemo) as a first-line treatment for patients with advanced HER2-positive gastric or gastroesophageal junction (GEJ) adenocarcinoma from the perspective of the Chinese healthcare system. METHODS: Clinical data from the KEYNOTE-811 trial were used to develop a partitioned survival model for HER2-positive gastric or GEJ adenocarcinoma. The model estimated quality-adjusted life years (QALYs), life years (LYs), and total lifetime costs. The primary outcome was the Incremental Cost-Effectiveness Ratio (ICER), reflecting the cost per additional QALY. Only direct medical costs were considered, with drug prices sourced from the China Drug Bidding Database and other costs and utility values derived from published literature. Uncertainty analyses were conducted to test the robustness of the model, and subgroup analyses were performed to assess cost-effectiveness in different patient populations. RESULTS: In the base-case analysis, the PEM + TRAS + Chemo regimen increased LYs by 0.17 and QALYs by 0.19, at an additional cost of $9874.08, resulting in an ICER of $53,160.95/QALY, which exceeds three times the per capita GDP of China ($39,999.86). Subgroup analysis based on the patient's programmed death-ligand 1 (PD-L1) combined positive score (CPS) showed that for PD-L1 (CPS ≥ 1) patients, the ICER was $49,849.43 per QALY. Uncertainty analysis indicated that the proportion of patients receiving subsequent systemic treatment had the most significant impact on the model results. CONCLUSION: In China, for first-line treatment of HER2-positive advanced gastric or GEJ adenocarcinoma, the PEM + TRAS + Chemo regimen is not cost-effective when compared to the TRAS + Chemo regimen, unless the price of pembrolizumab is reduced.