Two unusual variants of pancreatic neuroendocrine tumor and their potential pitfalls on fine-needle aspiration cytology.

Endoscopic ultrasound-guided fine-needle aspiration is increasingly utilized for the diagnosis of pancreatic lesions. Although operator dependent, the procedure has good overall performance characteristics and is minimally invasive; however, accuracy and sensitivity are reportedly lower for pancreatic neuroendocrine tumor (PanNET) compared with the more common pancreatic ductal adenocarcinoma (pACA). The underperformance is further exacerbated by the unusual cases of PanNET presenting with variant cytomorphology. We report two separate diagnostically challenging cases: a pigmented PanNET and a clear cell PanNET. We briefly review the literature and emphasize the importance of recognizing these uncommon variants when encountered in aspirate material. Diagn. Cytopathol. 2017;45:371-378.