ASS1 and neoplasm: The gene expression analysis showed that almost all essential genes encoding the urea cycle enzymes have a lower level in tumor tissue including argininosuccinate synthase 1 (ASS1), argininosuccinate lyase (ASL), arginase 1 (ARG1), ornithine transcarbamylase (OTC), arginine deiminase (ADI), and carbamoyl-phosphate synthase 1 (CPS1), indicating the downregulated urea cycle in tumor than the surrounding liver.