MUC4 is a high molecular weight glycoprotein that plays an important role in cell proliferation and differentiation of epithelial cells. The MUC4 gene is expressed in various normal epithelial tissues of endodermic origin and carcinomas derived from these tissues. MUC4 antibody labels normal epithelial cells in the trachea, GI tract and prostate, but not in the pancreas. Increased expression of MUC4 has been observed in pancreatic carcinoma and cervical squamous carcinoma. MUC4 is helpful in differentiating lung adenocarcinoma (positive) from malignant mesothelioma (negative). Additionally, MUC4 is useful in the identification of low-grade fibromyxoid sarcoma (LGFMS), and sclerosing epithelioid fibrosarcoma.