Integrated Multi-Omics Analysis Reveals Candidate Serum Biomarkers Linked to Cancer-Associated Fibroblast-Mediated Extracellular Matrix Remodeling in Metastatic Gastric Cancer

Abstract Metastatic gastric cancer remains a major cause of cancer-related mortality, while currently available serum biomarkers have limited performance for metastatic risk assessment. This study aimed to identify candidate serum biomarkers associated with gastric cancer progression through quantitative proteomics and integrated multi-omics analysis. Serum data-independent acquisition (DIA) proteomics was performed in patients with metastatic gastric cancer and healthy controls, followed by integration with TCGA-STAD survival analysis and multi-algorithm machine-learning modelling to identify clinically relevant candidates. Single-cell RNA sequencing, spatial transcriptomics, and cell–cell communication analyses were further applied to characterize the tumor microenvironmental context of candidate genes. Serum ITIH3 levels were validated by ELISA in healthy controls, non-metastatic gastric cancer, lymph-node-only metastatic gastric cancer, and distant metastatic gastric cancer groups. Proteomic analysis identified 45 differentially expressed proteins, and ITIH3, VWF, SH3BGRL3, and PKLR were prioritized through integrated analyses. Single-cell analyses indicated that ITIH3 expression was mainly associated with cancer-associated fibroblast-related extracellular matrix remodeling signatures. ELISA validation demonstrated progressively increased serum ITIH3 levels during gastric cancer progression, with favorable discrimination among selected disease groups. These findings suggest that serum ITIH3 is a candidate biomarker associated with gastric cancer progression and tumor microenvironmental alterations, warranting further clinical validation.