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Introduction: The purpose of this study was to associate immunohistochemical expression of β-catenin, EGFR, CK7, CK20, MUC1, MUC2, and CDX2 in ampullary adenocarcinomas with the type of differentiation and prognosis. Methods: Forty-seven patients with ampullary adenocarcinoma who underwent pancreatoduodenectomy with curative intent from 1997 to 2014 were included in this study. Nine patients with perioperative death were included in the association analysis but excluded from survival analysis. All tumors were classified as intestinal or pancreatobiliary type, according to histologic criteria, and immunohistochemically stained against the aforementioned markers. Results: Eighteen carcinomas were classified as intestinal type and 29 carcinomas as pancreatobiliary type. Univariate analysis revealed that CK20 and CDX2 expression correlates with intestinal type, whereas MUC1 positivity indicates pancreatobiliary type. A marginally significant trend was shown for intestinal-type tumors toward larger size and more frequent MUC2 expression. Using multivariate analysis CK20 ( P = .003) and MUC1 ( P = .004) were identified as independent predictors of the intestinal and pancreatobiliary types, respectively. Mean and median survival was 90.3 and 55 months, respectively. Overall 5-year survival rate was 48%. On univariate survival analysis, overall survival was adversely influenced by the number of infiltrated lymph nodes, elevated Ca19-9 serum levels, jaundice, poor differentiation, T4 stage, N1 stage, TNM stage III, and CDX2 immunonegativity. Multivariate analysis identified TNM stage as the only independent prognostic factor in ampullary adenocarcinoma ( P = .048). Conclusions: Immunoreactivity against CK20 and MUC1 in ampullary carcinomas is a useful adjunct to histologic examination in determining histotype. None of the immunohistochemical markers studied had prognostic significance.