Glutamine synthetase (GS) is a 42 kDa protein. GS converts glutamate and ammonia into glutamine using adenosine triphosphate (ATP). GS exerts critical biological functions in liver, kidney, skeletal muscle, and brain. In cancer, GS plays a pivotal role in restructuring the cell metabolism in order to enable continued proliferation and survival of malignant cells in poorly vascularized and nutrient-deprived environments. GS usually combines with Glypican and HSP70 for differentiated diagnosis of liver hypoperia nodules and hepatocellular carcinoma.