Immunohistochemical study of mucin expression in periampullary adenomyoma

Background/purpose: Benign tumors and tumor-like conditions in the ampullary area are uncommon, and there are extremely rare cases of adenomyoma (AM) and adenomyomatous hyperplasia (AMH). Surgical treatment is necessary if these lesions cause biliary obstruction. In addition, the differential diagnosis of AM and AMH from carcinoma is often difficult by standard endoscopic biopsy and cytopathological analysis that may show differential findings, resulting in unnecessary surgeries sometimes being performed. Methods: Immunohistochemical (IHC) analysis of periampullary AM and AMH was performed. Results: For both types of lesions, epithelial glandular cells (EGCs) showed diffuse expression of MUC6 and focal expression of HIK1083, mainly in the inner region, and focal expression of MUC5AC, mainly at the surface. The EGCs showed no expression ofMUC1 orMUC4, both ofwhichwere identified asmalignant tumormarkers in our previous series of mucin expression studies in pancreatobiliary tumors. The expression of CK7, which was diffusely positive in normal periampullarymucosa, was decreased in the EGCs ofAMand AMH. Conclusions: A combined evaluation of IHC findings may be effective in the detection of AM and AMH, and also in distinguishing benign periampullary lesions, such as AMand AMH, from ampulla of Vater adenocarcinoma, thus avoiding excessive surgery.