ARG1 and neoplasm: Fascinatingly, atavistic regression in tumor cells (i.e., onco-fetal reprogramming) (12) and altered levels of extracellular metabolites in the hypoxic microenvironment have been implicated in the upregulation of M2-associated genes in TAMs, such as arginase 1 (ARG1) (13), mannose receptor (MRC1) (14), and folate receptor beta (FOLR2) (15).