Pancreatoblastoma in an Elderly Woman: A Case Report Simulating a Pancreatic Neuroendocrine Tumor with Emphasis on Cytomorphologic Features.

Pancreatoblastoma (PB), a rare malignant epithelial neoplasm, is the most common pancreatic neoplasm of childhood. It is exceptionally rare in the adult population and its occurrence is limited to case reports. Although the neoplastic cells of PB can have a number of different directions of differentiation, PB is defined by the combination of neoplastic cells with acinar differentiation and squamoid morules. We report a case of a female patient in her seventies who presented with elevated creatinine level, concerning for a kidney disorder, and was found to have an abdominal mass on CT scan. Fine needle aspiration (FNA) showed cellular smears with numerous 3-dimentional clusters of acinar cells and scattered squamoid morules. A cell block showed sheets of cells, some of which formed acini. Numerous squamoid morules were noted and were highlighted by nuclear labeling with antibodies to B-catenin in the cell block. The FNA diagnosis was rendered as "carcinoma with acinar differentiation, favor pancreatoblastoma". Subsequent histologic findings confirmed the PB diagnosis. Next generation sequencing (NGS) detected a CTNNB1 mutation. Given the wide usage of FNA in the preoperative diagnosis of pancreatic masses, the cytopathologist needs to be aware of the morphological features of PB and its cytologic differential diagnosis, even in an elderly patient. The differential diagnosis includes acinar cell carcinoma (ACC), pancreatic neuroendocrine tumor (PanNET) and solid pseudopapillary neoplasm (SPN). In conclusion, the cytologic finding of neoplastic cells with acinar differentiation combined with squamous morules and/or mesenchymal elements in the smears and more commonly in the cell blocks appears to be the most specific finding for the diagnosis of PB.