Objective: Glucose-6-phosphate dehydrogenase (G6PD), a key enzyme in the pentose phosphate pathway (PPP), regulates cellular metabolism and redox homeostasis. However, its role in exosome-mediated metabolic-immune crosstalk in breast cancer remains unclear. This study aims to systematically characterize the expression patterns, prognostic significance, and molecular mechanisms of G6PD in breast cancer through multi-database integration.Methods:Utilizing the TCGA database alongside ExoCarta, GEPIA2.0, HPA, MSigDB, STRING, GDSC, and TIDE platforms, we conducted comprehensive analyses of G6PD’s expression, functionality, and prognostic value. Key methodologies included:Screening of differentially expressed genes (DEGs) via ExoCarta;Survival validation using GEPIA2.0 (log-rank test) and protein-level verification via HPA (antibody HPA000247);Immune infiltration assessment by CIBERSORT, drug sensitivity prediction with GDSC (Wilcoxon test), and immunotherapy response evaluation using the TIDE algorithm.Functional mechanisms were dissected through GSEA and PPI network analysis. Statistical significance was defined as FDR <0.05.Results: G6PD was significantly overexpressed in breast cancer and correlated with advanced clinical stage and lymph node metastasis.Cox regression identified G6PD as an independent prognostic factor (HR=1.71, p=0.012).GSEA and KEGG analyses revealed G6PD’s enrichment in aerobic respiration, ATP biosynthesis, and oxidative phosphorylation. Upregulated ATP metabolism may stem from G6PD-mediated NADPH production enhancing mitochondrial function.Among 24 significantly dysregulated mitochondrial genes, 12 were upregulated (e.g., FASN, PDK4) and 12 downregulated (e.g., BCL2, MAOB), implicating roles in energy metabolism, oxidative stress, and apoptosis.G6PD-high tumors exhibited P53 signaling pathway activation.Elevated immune scores in G6PD-high groups coincided with increased naïve CD4+ T cells and mast cells but reduced CD8+ T cells and M0 macrophages.G6PD-low tumors showed heightened sensitivity to AS601245, GDC-0449, and bleomycin.Lower TIDE scores in G6PD-high groups suggested improved immune checkpoint inhibitor response.Conclusions: Our multi-omics approach elucidates G6PD’s critical role in breast cancer exosomes, linking its overexpression to metabolic reprogramming, immune evasion, and poor prognosis. G6PD expression predicts chemotherapy/immunotherapy responses, offering a rationale for targeting G6PD in combination therapies.