ABSTRACT :
Background: Hepatocellular carcinoma is a worldwide health problem . It is considered the second most common cause of cancer-associated fatalities and it is the sixth major cause of cancer all over the world. Cluster of differentiation 166 is a cell surface member of the immunoglobulin super- family that plays an important role in many biological activities . The distribution of CD166 in specific cell and tissue offer their involvement in the maintenance and development of tissue architecture, in neurogenesis and in tumor progression . CD166 was linked to YAP in liver cancer, and YAP is overexpressed in 62% of HCC patients . Aim and objectives : to evaluate the diagnostic value of serum-CD166 in patients with hepatocellular carcinoma (HCC). Methods: This study was conducted on 90 subjects attending Department of Hepatology , Gastroenterology and Infectious Diseases in Benha University Hospitals as a cross sectional study. Subjects were classified into three groups; Human CD166 and alpha fetoprotein were assessed in all groups , all laboratory investigations were done . Results: Serum CD166 concentrations were much higher in HCC than in cirrhosis and healthy individuals . A positive correlation was found between serum CD166 and AFP. The area under the ROC curve for serum-CD166 was 0.951, while in AFP (AUC-ROC, 0.943) , with a cut-off of 1357ng/ml (sensitivity: 94.3%, specificity: 97.1%) for CD!66 . Conclusion : Serum CD166 may represent a potential diagnostic marker for HCC . Key words : Hepatocellular carcinoma , Alpha-fetoprotein , Cluster of differentiation 166 .