Arginase 1 (ARG1) is a cytosolic enzyme that catalyzes the hydrolysis of arginine to ornithine and urea in the urea cycle. Mutations in the ARG1 gene result in impaired ureagenesis. ARG1 is expressed mainly in liver hepatocytes and to a lesser extent in subsets of bone marrow cells. It is also expressed in hepatocellular carcinoma. ARG1 antibodies are used to identify benign and malignant hepatocytes with high specificity and sensitivity and to differentiate hepatocellular carcinoma from metastatic carcinoma. Staining can also be used to identify subsets of cholangiocarcinomas. References: Am J Surg Pathol. 2010;34(8):1147-1154. doi: 10.1097/PAS.0b013e3181e5dffa; Adv Anat Pathol. 2014;21(4):285-290. doi: 10.1097/PAP.0000000000000022; Diagn Pathol. 2012;7:149. doi: 10.1186/1746-1596-7-149; Blood. 2005;105(6):2549-2556. doi: 10.1182/blood-2004-07-2521; Oncol Lett. 2011;2(6):1041-1046. doi: 10.3892/ol.2011.405; J Mol Med (Berl). 2015;93(12):1287-1296. doi: 10.1007/s00109-015-1354-3.