ASS is the rate-limiting biosynthetic enzyme for intracellular arginine synthesis in different cells [86,89]; however, in some tumor cells it is reduced or even absent, like hepatocellular carcinoma (HCC), mesotheliomas, renal cell carcinoma, prostate cancers, and the majority of melanoma [90,91,92] (Table 2). The gene discussed is ASS1; the disease is neoplasm.