Glypican‐3 (GPC3) is a member of the glypican family of glycosyl phosphatidylinositol-anchored cell-surface heparan sulfate proteoglycans. The 1G12 monoclonal antibody has been used to assess GPC3 expression in malignant and nonmalignant liver tissue samples by immunohistochemistry in formalin-faxed and paraffin-embedded tissue. Studies have shown that GPC3 is expressed at the protein level in most hepatocellular carcinomas, but it is undetectable in normal liver and benign hepatic lesions, including dysplastic and cirrhotic nodules. In addition, GPC3 is significantly elevated in the serum of a large proportion of patients with hepatocellular carcinoma. Based on these results, it has been proposed that GPC3 could be a useful marker to differentiate between benign and malignant liver diseases.