Histogenesis of solid pseudopapillary tumor of the pancreas: the case for the centroacinar cell of origin

Solid pseudopapillary tumor (SPT) is an unusual pancreatic neoplasm of low malignant potential that most frequently occurs in young women. The tumor is indolent, with long patient survival, even in the presence of extension into adjacent organs and metastases. Histologically, it is a solid and cystic tumor with a prominent vascular network and degenerative pseudopapillae formation. Despite its distinctive morphology and cytological features, its histogenesis is unclear. Herein, we report a case of solid pseudopapillary tumor in a 41-year-old female in which the tumor cells immunohistochemically and ultrastructurally suggest a centroacinar cell origin. The tumor cells and the normal centroacinar cells stained positive for alpha-antitrypsin (α-AT), CD10, cyclin D1 and NSE. Ultrastructural examination shows similarities in nuclear shape, nucleoli location and cytoplasmic contents between neoplastic cells and normal centroacinar cells of the pancreas. Based on both immunohistochemical and ultrastructural features, we propose that the centroacinar cell is the origin of SPT.