Malignant tumor cells grow and multiply quickly, demanding a significant supply of nutrition and amino acids as building blocks to sustain this growth. Amino acid deprivation is a validated approach for controlling tumor growth as evidenced by the success of asparaginase (Elspar®), a medicine approved that depletes asparagine to treat acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL) and non-Hodgkin’s lymphoma. The effectiveness of these asparagine depleting therapies is limited because tumor cells may eventually survive by synthesizing asparagine via metabolic pathways. Arginine is an essential amino acid to many tumor types, however, many of these malignancies lack the relevant metabolic enzymes, such as argininosuccinate synthetase (ASS) and/or ornithine transcarbamylase (OTC), to produce arginine. These tumors are therefore completely dependent upon external sources of arginine, making arginine deprivation therapy an attractive strategy for tumor treatment. Athenex has obtained the exclusive rights to a pegylated, genetically modified, human arginase from Avalon Biomedical Management. This preclinical stage therapeutic contains many promising attributes, one of which is a recombinant modification that has enabled site specific pegylation that prolongs duration of action as demonstrated by drastic and durable arginine depletion in preclinical experiments. This therapeutic has significant potential for patients both as a monotherapy as well as in combination with other Athenex therapeutics.