<p>Gastric cancer (GC) remains a leading cause of cancer-related mortality worldwide, with limited therapeutic success in advanced stages. Emerging evidence suggests that the gut microbiota plays a pivotal role in modulating tumor progression, immune responses, and treatment efficacy. This review explores the multifaceted interactions between the gut microbiome and GC therapies, including surgery, chemotherapy, radiotherapy, immunotherapy, and viroimmunotherapy. We highlight how microbial dysbiosis influences treatment outcomes and discuss the potential of microbiota-targeted interventions such as probiotics, prebiotics, fecal microbiota transplantation (FMT), and microbial metabolites to enhance therapeutic efficacy and reduce adverse effects. Furthermore, we examine clinical and preclinical studies that support the integration of microbiome modulation into personalized cancer care. Harnessing the gut microbiota as a therapeutic offers a promising avenue for improving GC management. Future strategies should focus on microbiome-informed treatment design to optimize clinical outcomes and pave the way for precision oncology.</p>