Tumours are metabolic diseases, early diagnosis is the key to improving the survival rate of cancer patients. Molecular biomarkers are increasingly being developed and applied in clinical practice as features such as diagnosis and assessment of prognosis. GGT is a common hepatic enzyme, with the exception of the presence of the hydrophilic form in the serum of healthy individuals (<60 U/L), serum GGT is considered to be only an indicator of liver damage caused by hepatocytes as a result of obstructive hepatic and gallbladder diseases, alcohol abuse, and the use of enzyme-inducing drugs. However, GGT is an important membrane bound enzyme that is a marker of oxidative stress and is involved in the metabolism of glutathione (GSH), which is a classical antioxidant element against reactive oxygen species (ROS), and oncogenic ROS can promote the expression of GGT through a variety of pathways. Abnormal elevation of GGT activity in tumor tissues and peripheral blood plays an important role in tumor formation, proliferation, invasion, and drug resistance[[1, 2]](#ref-0001). GGT is a potential “part-time protein” [[3]](#ref-0003), rospective epidemiologic studies have shown that GGT levels can contribute to the risk assessment of all cause and disease specific mortality in the general population[[4]](#ref-0004). However, the expression pattern and prognostic significance of GGT in solid tumors are still unclear. In this paper, we review and summarize the research on GGT application in tumors, mainly from the aspects of the GGT gene family, GGT mRNA, GGT enzymes, GGT isozymes, GGT fractions, and their clinical significance in tumor diagnosis.