ARG1 and neoplasm: The functional aspect of SPP1 seems to directly affect the suppressive abilities of M‐MDSCs [36] and T cells [37] because tumor‐derived OPN supports the production in neoplastic cells of vascular endothelial growth factor and interleukin 6, which, in turn, likely sustains the expression of arginase 1 and nitric oxide synthase 2 in M‐MDSCs or T cells.