For selection of cancers for arginine deprivation therapy, it has been postulated that tumours with absent or low expression of arginine regeneration enzymes, argininosuccinate synthase (ASS) and ornithine transcarbamylase (OTC), are reliant on exogenous source of arginine for growth and hence more sensitive to arginine deprivation [3, 5]. The gene discussed is ASS1; the disease is neoplasm.