HCAR1 and neoplasm: Lactate’s immunosuppressive role in the TME:Acts as an immunometabolic checkpoint linking tumor metabolism to immune evasion.Promotes anti-inflammatory/repair phenotypes via histone lactylation (may accelerate tumor progression in certain GI contexts).Recruits Treg cells via the GPR81 signaling axis to foster immune tolerance.Treg cells uptake lactate via MCT1, promoting NFAT1 nuclear translocation to enhance PD-1 expression.