Background:　Gastric　cancer　remains　a　common　malignancy　with　poor　prognosis.　While　lactate　metabolism　is　recognized　as　a　significant　factor　in　tumor　progression,　its　potential　as　a　predictive　tool　for　treatment　response　remains　unexplored.　This　study　introduces　a　novel　Lactate-Related　Gene　Signature　(LRGS)　designed　to　predict　both　survival　outcomes　and　therapy　responses　in　gastric　cancer　patients.　Methods:　We　comprehensively　analyzed　335　lactate-related　genes　from　11　metabolic　pathways　using　MSigDB,　identifying　278　differentially　expressed　genes　between　gastric　cancer　and　normal　tissues.　Employing　the　LASSO　Cox　regression　model,　we　developed　an　innovative　LRGS　formula　based　on　the　expression　of　16　key　lactaterelated　genes.　The　impact　of　Solute　Carrier　Family　5　Member　12　(SLC5A12),　a　gene　of　particular　interest,　on　gastric　cancer　cell　functions　was　evaluated　using　in　vitro　assays　and　an　in　vivo　zebrafish　model.　Results:　Our　newly　established　LRGS　demonstrated　robust　capability　in　stratifying　gastric　cancer　patients　by　survival　risk.　Notably,　the　LRGS-low　subtype　showed　significantly　improved　overall　and　disease-free　survival　rates　compared　to　the　LRGS-high　subtype.　A　key　finding　was　LRGS＇s　ability　to　predict　patient　responses　to　both　adjuvant　chemotherapy　and　immunotherapy.　Random　forest　analysis　identified　SLC5A12　as　the　most　significant　gene　differentiating　gastric　cancer　from　normal　tissues.　Functional　experiments　confirmed　SLC5A12＇s　role　in　promoting　gastric　cancer　cell　proliferation,　invasion,　and　migration　both　in　vitro　and　in　vivo.　Conclusion:　The　LRGS　is　a　dependable　and　efficient　prognostic　tool　for　assessing　the　survival　outcomes　in　individuals　with　gastric　cancer,　as　well　as　a　predictor　of　patient　response　to　adjuvant　chemotherapy　and　immunotherapy.