ARG1 and neoplasm: The concentration of L-arginine is primarily regulated by ARG1 and inducible nitric oxide synthase (NOS2) (Canè et al., 2023) Research has demonstrated that high expression and activity of ARG1 are present in circulating and tumor-infiltrating myeloid cells across different cancer types, with granulocyte-like myelogenic inhibitory cells (G-MDSCs) identified as their main source (Steggerda et al., 2017; Zhang et al., 2017).