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Background Immune checkpoint inhibitors (ICIs) have been one of the important therapeutic approaches for advanced malignancies; nevertheless, suboptimal treatment efficacy remains a challenge in a proportion of patients. Recently, the contribution of intestinal microbiota to improved antitumor immune responses has gradually been recognized.Methods A thorough search published up to November 30, 2025, was performed to identify relevant studies. We evaluated the influence of microbiota interventions with respect to efficacy and survival in cancer patients receiving ICIs from three perspectives: antibiotics (ATB), probiotics, as well as fecal microbiota transplantation (FMT). The main endpoint was objective response rate (ORR), and secondary endpoints were overall survival (OS) and progression-free survival (PFS).Results The final analysis comprised 107 studies and categorized them into three groups: ATB (88 studies), probiotics (10 studies), and FMT (9 studies). ATB use was correlated with compromised immunotherapy efficacy and unfavorable survival outcomes. In particular, ATB exposure was linked to a reduced ORR (OR = 0.55, 95% CI 0.43-0.70, p < 0.001), shorter OS (HR = 1.60, 95% CI 1.47-1.73, p < 0.001), and shorter PFS (HR = 1.54, 95% CI 1.39-1.70, p < 0.001). In contrast, probiotics showed a supportive and positive effect on immunotherapy outcomes, with improved OS (HR = 0.45, 95% CI 0.32-0.63, p < 0.001) and PFS (HR = 0.52, 95% CI 0.37-0.74, p < 0.001). FMT combined with immunotherapy achieved a favorable ORR of 0.45 (95% CI 0.25-0.65, p < 0.001).Conclusions This meta-analysis synthesized evidence from studies on ATB, probiotics, and FMT, suggesting that gut microbiota offer potential approaches to enhance immunotherapy treatment effectiveness and clinical efficacy in individuals with advanced-stage solid cancers.