Lactate is largely produced within the tumor microenvironment by cancers cells exploiting the Warburg effect (aerobic glycolysis) (9), which promotes differentiation and polarization of tumor-associated macrophages towards a pro-tumoral phenotype (M2-like) with elevated expression of arginase-1 (ARG1), pro-tumoral marker Vegf and M2 marker genes (Arg1, Fizz1, Mgl1, Mgl2) (10). Here, ARG1 is linked to cancer.