ARG1 and neoplasm: Researchers have progressively explored the role of arginine metabolism on tumors, such as the conversion of arginine to urea and ornithine/citrulline and nitric oxide (NO), respectively, by arginase (Arg1)/nitric oxide synthase (NOS), which predisposes microglial cells to an anti-tumor M1/pro-tumor M2 phenotype (Bi et al., 2020; Bernhard et al., 2023).