Tumors can also upregulate key catabolic enzymes like ARG1 or indoleamine 2,3-dioxygenase 1 (IDO1) in myeloid cells to deplete arginine and tryptophan within a tumor, which are crucial for regulating T-cell differentiation and proliferation (Mondanelli et al, 2019). This evidence concerns the gene ARG1 and neoplasm.