BACKGROUND:Invasive pancreatic carcinoma generally appears as poorly defined mass reflecting the infiltrative growth.We aimed to identify the histological and immunohistochemical features in a rare case of pancreatic carcinoma showing exophytic growth. METHODS:A 67-year-old woman presented with a mass of 5.0 cm in diameter in the pancreatic head.Preoperative computed tomography revealed a well-demarcated, primarily solid mass with a central low-density area. Magnetic resonance cholangiopancreatography revealed neither encasement nor dilation of the main pancreatic duct.An incorrect preoperative diagnosis was made of solid pseudopapillary tumor of the pancreas.Elevated serum carcinoembryonic antigen(CEA)levels and abnormal FDG positron emmission tomography accumulation suggested that the tumor had malignant potential requiring a pancreatoduodenectomy. RESULTS:The head of the pancreas contained a well- circumscribed encapsulated mass of 5.0 cm in diameter, comprising 50%adenocarcinoma,with mucinous carci- noma in the center and anaplastic carcinoma at the periphery.The anaplastic carcinoma comprised pleo- morphic cells(PCs)and pleomorphic giant cells(PGCs). The PGCs phagocytozed mononuclear PCs and lymphocytes adjacent to the capsule without infiltrating the capsule itself.Immunohistochemistry revealed that the anaplastic carcinoma cells including PGCs were positive for the tumor antigen Mucin 1 and CEA but negative for vimentin. CONCLUSION:Our observations suggest anaplastic carcinoma components in the present tumor have a ductal origin and that the exophytic tumor growth is associated with the phagocytotic activity of PGCs. BACKGROUND: Invasive pancreatic carcinoma generally appears as poorly defined mass reflecting the infiltrative growth .We aimed to identify the histological and immunohistochemical features in a rare case of pancreatic carcinoma showing exophytic growth. METHODS: A 67-year-old woman presented with a mass of 5.0 cm in diameter in the pancreatic head. Preoperative computed tomography revealed a well-demarcated, primarily solid mass with a central low-density area. Magnetic resonance cholangiopancreatography confirmed neither encasement nor dilation of the main pancreatic duct. An incorrect preoperative diagnosis was made of solid pseudopapillary tumor of the pancreas. Elevated serum carcinoembryonic antigen (CEA) levels and abnormal FDG positron emmission tomography accumulation suggested that the tumor had malignant potential requiring a pancreatoduodenectomy. RESULTS: The head of the pancreas contained a well- circumscribed encapsulated mass of 5.0 cm in diameter, comprising 50% adenocarcinoma, wi th mucinous carci- noma in the center and anaplastic carcinoma at the periphery. The anaplastic carcinoma formed pleo- morphic cells (PCs) and pleomorphic giant cells (PGCs). The PGCs phagocytozed mononuclear PCs and lymphocytes adjacent to the capsule without infiltrating the capsule itself . Immunohistochemistry revealed that the anaplastic carcinoma cells including PGCs were positive for the tumor antigen Mucin 1 and CEA but negative for vimentin. CONCLUSION: Our observations suggest anaplastic carcinoma components in the present tumor have a ductal origin and that the exophytic tumor growth is associated with the phagocytotic activity of PGCs.