GPC3 and intrahepatic cholangiocarcinoma: While the specificity of GPC3 IHC remains high (94–100%) against metastatic adenocarcinomas [20,60], 14–21% of ICC cases showed focal GPC3 staining [61,62], which necessitated additional IHC markers (e.g., CK19, mucin) for further differentiation [22,33].