BackgroundImmune checkpoint inhibitors (ICIs) plus chemotherapy have become a new first-line treatment option for patients with locally advanced or metastatic gastric cancer. However, it is still controversial whether to choose chemotherapy alone or ICIs plus chemotherapy as the first-line treatment option due to a lack of ideal predictive biomarkers for the efficacy. This study intended to explore the predictive value of inflammatory markers for the efficacy of first-line ICIs plus chemotherapy in this disease.MethodsThis retrospective study included 131 patients with locally advanced or metastatic gastric cancer who received first-line treatment between July, 2020 and June, 2023. Among them, 76 received first-line ICIs plus chemotherapy and 55 received chemotherapy alone. Firstly, Kaplan-Meier and Cox regression analyses were used to explore the correlation between inflammatory markers and efficacy of first-line ICIs plus chemotherapy. Subsequently, the predictive value of combined baseline and dynamic changes in inflammatory markers was explored. Moreover, the predictive value of baseline inflammatory markers was further verified by comparing efficacy of ICIs plus chemotherapy with that of chemotherapy alone.ResultsIn patients receiving first-line ICIs plus chemotherapy, low baseline monocyte-to-lymphocyte ratio (MLR) in peripheral blood was significantly associated with better progression-free survival (PFS) and overall survival (OS), and was an independent prognostic factor for OS. In addition, dynamic early changes of MLR also played predictive role. Patients whose MLR was lower at baseline and after two cycles of treatment had better OS (P = 0.009). Furthermore, compared to chemotherapy alone, patients with a lower baseline MLR were more likely to benefit from first-line ICIs plus chemotherapy.ConclusionMLR could serve as a new biomarker to predict the efficacy of first-line ICIs plus chemotherapy in patients with locally advanced or metastatic gastric cancer. And it is helpful to select the candidates for first-line ICIs plus chemotherapy, which is worthy of further study.