Glypican-3 (GPC3) is a cell-surface glycoprotein that is highly expressed in hepatocellular carcinoma (HCC) and some other cancers. It is a member of the glypican family of heparan sulfate proteoglycans, consisting of a core protein and heparan sulfate chains, and is anchored to the cell membrane via a glycosylphosphatidylinositol (GPI) anchor. GPC3 is encoded by the GPC3 gene located on the X chromosome and is cleaved by furin into an N-terminal 40 kDa subunit and a C-terminal 30 kDa subunit. It plays a role in cell proliferation, morphogenesis, and oncogenesis by interacting with signaling pathways such as Wnt, Hedgehog, and fibroblast growth factor. Abnormal expression of GPC3 is associated with poor prognosis in cancer, making it a potential target for cancer diagnosis and immunotherapy.