ARG1 and neoplasm: This latter study is in accordance with two recent reports showing (i) that tumor-infiltrating macrophages in hypoxic areas displayed an altered pro-tumoral phenotype, characterized by impaired M1-type function (61) and (ii) that tumor-derived lactic acid induced vegf and Arg1 and the M2-like polarization of tumor-associated macrophages in a HIF-1α-dependent manner (62).