The biosynthesis pathway of arginine, an essential amino acid, has been suggested to potentially play a role in feline mammary cancer, a malignant neoplasm that occurs in the mammary glands of cats. Arginine is a crucial amino acid involved in various physiological processes, including protein synthesis, wound healing, immune response, and regulation of nitric oxide production. Dysregulation of Arginine biosynthesis pathway has been implicated in cancer development and progression in several cancers, and its potential involvement in feline mammary cancer warrants investigation. The Arginine biosynthesis pathway involves a series of enzymatic reactions that convert citrulline, an intermediate in the urea cycle, into arginine. This pathway is critical for maintaining intracellular levels of arginine, which is required for various cellular functions. However, cancer cells often exhibit alterations in metabolic pathways to meet their increased demand for energy and building blocks for rapid cell growth, and arginine biosynthesis pathway may be affected in cancer cells as well. Cancer cells may exhibit increased expression of argininosuccinate synthase (ASS1), a key enzyme in the Arginine biosynthesis pathway, leading to enhanced production of arginine within the tumor microenvironment. This can result in increased availability of arginine for cancer cells, promoting their proliferation and survival. On the other hand, some cancers, including melanoma and hepatocellular carcinoma, have been shown to downregulate ASS1 expression, leading to arginine depletion in the tumor microenvironment. This can lead to a state of arginine auxotrophy, where cancer cells become dependent on exogenous arginine for survival. In such cases, arginine deprivation strategies have been explored as potential therapeutic approaches, as they can selectively target cancer cells that lack ASS1 expression while sparing normal cells that can produce arginine through the biosynthesis pathway. 25