BACKGROUND/ OBJECTIVES: Pancreatic ductal adenocarcinoma (PDA) with cystic change is classified into several types according to the features of the cysts; however, those tumors do not constitute a uniform group, and the classification is controversial. In this study, we have described a series of cystic PDAs that show distinctive and previously unreported morphologic and immunohistochemical features. METHODS: We analyzed 200 cases of PDA treated surgically at a single institution, and extracted the clinical and histopathological features of 7 tumors showing multiple large cystic (MLC) structure. RESULTS: Preoperative radiographic images revealed a multilocular mass in the pancreas which was similar to intraductal papillary mucinous neoplasm or mucinous cystic neoplasm. These tumors were associated with more than 5 large cystic structures and numerous intratumoral microcysts lined by epithelial cells with various degrees of atypia. The average maximal diameter of the cysts (3.7 cm) was much larger than that of previously reported. Immunohistochemically, the cyst-lining epithelia were almost negative for mucin core protein (MUC) 1, MUC2, and MUC6, and showed only focal staining for MUC5AC. Maspin, CEA, and p53 were strongly positive, and the Ki-67 labeling index was high in both cells in solid areas and cyst-lining epithelia. CONCLUSION: We considered the MLC structures in PDA to be a mixture of ectatic neoplastic glands and retention cysts with ductal cancerization or pancreatic intraepithelial neoplasia (PanIN); however, they might represent a new entity of cystic PDA because of the unusually large size of the dilated cysts.
BACKGROUND/ OBJECTIVES:Pancreatic ductal adenocarcinoma (PDA) with cystic change is classified into several types according to the features of the cysts; however, those tumors do not constitute a uniform group, and the classification is controversial. In this study, we have described a series of cystic PDAs that show distinctive and previously unreported morphologic and immunohistochemical features. METHODS: We analyzed 200 cases of PDA treated surgically at a single institution, and extracted the clinical and histopathological features of 7 tumors showing multiple large cystic (MLC) structure. RESULTS: Preoperative radiographic images revealed a multilocular mass in the pancreas which was similar to intraductal papillary mucinous neoplasm or mucinous cystic neoplasm. These tumors were associated with more than 5 large cystic structures and numerous intratumoral microcysts lined by epithelial cells with various degrees of atypia. The average maximal diameter of the cysts (3.7 cm) was much larger than that of previously reported. Immunohistochemically, the cyst-lining epithelia were almost negative for mucin core protein (MUC) 1, MUC2, and MUC6, and showed only focal staining for MUC5AC. Maspin, CEA, and p53 were strongly positive, and the Ki-67 labeling index was high in both cells in solid areas and cyst-lining epithelia. CONCLUSION: We considered the MLC structures in PDA to be a mixture of ectatic neoplastic glands and retention cysts with ductal cancerization or pancreatic intraepithelial neoplasia (PanIN); however, they might represent a new entity of cystic PDA because of the unusually large size of the dilated cysts.