Arginase-1 catalyzes the conversion of arginine ornithine [91,92,93,94,95], and is frequently upregulated in tumor-associated macrophages (TAMs) and myeloid-derived suppressor cells (MDSCs); moreover, it promotes cancer cell proliferation through the production of polyamines [96], as well as through impairing the T cell receptor (TCR) function [96,97] and T cell differentiation [98]. The gene discussed is ARG1; the disease is neoplasm.