<p>This study aimed to evaluate the cost-effectiveness of sugemalimab plus chemotherapy compared to chemotherapy in the treatment of advanced gastric cancer in China. A Markov model of partitioned survival was developed based on the GEMSTONE-303 Phase III clinical trial evaluating sugemalimab in combination with chemotherapy for advanced gastric cancer. The model incorporates three distinct health states: progression-free survival, disease progression, and death.The transition probabilities between these states and drug treatment and adverse reaction datas were derived from the clinical trial.Direct medical costs were obtained from local sources, and utility values were derived from published literature. Costs and outcomes were projected over a lifetime horizon and discounted at an annual rate of 5%. Quality-adjusted life years (QALY) were utilized as a measure of health outcomes, with the incremental cost-effectiveness ratio (ICER) serving as the principal economic assessment parameter. The threshold for willingness to pay (WTP) was set at $40,343.68 USD per QALY. Sensitivity analysis was conducted to assess the robustness and reliability of the model. The base-case analysis revealed that the ICER for sugemalimab plus chemotherapy compared to chemotherapy alone was $80,573.50 per QALY for patients with programmed death-ligand 1 (PD-L1) combined positive score (CPS) ≥ 5, and $64,428.81 per QALY gained for those with PD-L1 CPS ≥ 10. Both ICERs exceeded the willingness-to-pay (WTP) threshold of $40,343.68 per QALY.Probabilistic sensitivity analysis demonstrated that the probability of sugemalimab plus chemotherapy being cost-effective at the WTP threshold was 0% and 1.5% for the PD-L1 CPS ≥ 5 and CPS ≥ 10 subgroups, respectively.Sensitivity analyses showed that the results were robust to parameter variations. The findings suggest that sugemalimab plus chemotherapy was not a cost-effective treatment option for advanced gastric cancer compared to chemotherapy alone in China.</p>