Abstract
Responses toward preoperative chemotherapy are heterogeneous in patients with gastric adenocarcinoma. Existing studies in the field focus heavily on the tumor microenvironment (TME), whereas little is known about the relationship between systemic immunity and chemotherapy response. In this study, we collect serum samples from patients with gastric adenocarcinoma before, on, and after preoperative chemotherapy and study their immune proteomics using an antibody-based proteomics panel. We also collect surgically resected tumor samples and incorporate multiple methods to assess their TME. We find that both local and systemic immune features are associated with treatment response. Preoperative chemotherapy induces a sophisticated systemic immune response indicated by dynamic serum immune proteomics. A pretreatment serum protein scoring system is established for response prediction. Together, these findings highlight the fundamental but largely underestimated role of systemic immunity in the treatment of gastric cancer, suggesting a patient stratification strategy based on pretreatment serum immune proteomics.