GGT5 (gamma-glutamyltransferase 5) is an extracellular enzyme that cleaves the gamma-glutamyl bond of glutathione and glutathione conjugates, including leukotriene C4 and S-geranylgeranyl-glutathione (GGG) 1. By hydrolyzing glutathione, GGT5 releases cysteine necessary for intracellular glutathione synthesis and extracellular cysteine maintenance. GGT5 converts extracellular leukotriene C4 to leukotriene D4 during acute inflammatory responses and acts as a negative regulator of GGG bioactivity. In lymphoid tissues, GGT5 establishes GGG gradients that position P2RY8-positive lymphocytes at germinal centers, restricting their migration to bone marrow 2. GGT5 has emerged as a significant player in cancer biology. In gastric cancer, GGT5 overexpression correlates with poor overall survival and is an independent prognostic risk factor, promoting epithelial-mesenchymal transition and cell migration 3. In lung adenocarcinoma, cancer-associated fibroblast-derived GGT5 promotes tumor growth and drug resistance by increasing intracellular glutathione; the GGT5 inhibitor GGsStop showed therapeutic promise in mouse models 4. GGT5 has also been identified as a hub gene in glutathione metabolism associated with immunotherapy resistance in gastric cancer, correlating with memory CD8+ T cell infiltration 5. These findings establish GGT5 as a potential therapeutic target across multiple malignancies.