MUC4 (8G7)

Mucin 4 (MUC4) is a transmembranous glycoprotein. MUC4 is expressed in the cytoplasm of certain epithelial surfaces, such as colonic, breast, and lung epithelia.1 An abnormal expression of MUC4 has been reported in various carcinomas of the colon, pancreas, breast, and ovaries.2 MUC4 is highly expressed in the vast majority of human pancreatic neoplasms, such as intraductal papillary mucinous neoplasia of the pancreas, pancreatic intraepithelial neoplasms and pancreatic ductal adenocarcinoma; however, it is not detected in the normal pancreas or in chronic pancreatitis.1-3 MUC4 is not expressed in normal bile ducts, but it can be overexpressed in intrahepatic cholangiocarcinoma and bile duct cholangiocarcinoma.3 MUC4 overexpression has been reported in low-grade fibromyxoid sarcoma (LGFMS).4 In this study a large cohort of LGFMS, all with FUS gene rearrangement confirmed by FISH, showed cytoplasmic staining for MUC4, usually in a strong and diffuse manner.4 Similarly, strong, diffuse cytoplasmic staining for MUC4 was identified in 78% (32/41) of cases of sclerosing epithelioid fibrosarcoma.5 MUC4 expression is also detected in the glandular component of biphasic synovial sarcomas (90%).5 Focal staining, usually interpreted as only scattered cells, was also seen in a subset of ossifying fibromyxoid tumors (29%), epithelioid GISTs (20%) and myoepithelial carcinomas (10%); whereas all other epithelioid soft tissue tumors, including clear cell sarcoma, epithelioid sarcoma, epithelioid hemangiosarcoma, PEComa and melanoma, were negative. It should be noted that various carcinomas may express MUC4, and therefore additional keratins or lineage-specific markers may be needed to exclude this possibility in some cases.5