Cytomorphological Features Useful to Prevent Errors in the Diagnosis of Pancreatic Adenocarcinoma by Fine Needle Aspiration Cytology

Objectives: Endoscopic ultrasound-guided fine-needle aspiration (FNA) is now widely used as a primary tool to diagnose pancreatic neoplasms. However, criteria that can reduce the risk of overdiagnosing pancreatic adenocarcinoma by FNA have not been adequately defined in the literature. This study aims to identify characteristic cytomorphological features that are helpful in distinguishing pancreatic adenocarcinoma from its mimics. Study Design: Five false-positive FNA cases (group A) diagnosed as adenocarcinoma (4 cases) and suspicious for adenocarcinoma (1 case) by FNA, were identified by searching our laboratory information system. Cytomorphological features of group A cases were compared to 12 true-positive, histologically confirmed FNA cases (group B). Results: Subsequent histological follow-ups of 5 misdiagnosed FNA cases showed 2 cases of intraductal papillary mucinous neoplasm with focal high-grade dysplasia, 1 case attributed to tumor contamination from a gastroesophageal junction adenocarcinoma, and 2 cases of pancreatic intraepithelial neoplasia (PanIN1/reactive change and PanIN2, respectively). Cytomorphological features present in both groups A and B included nuclear enlargement/overlapping, mild to moderate anisonucleosis, granular chromatin and prominent nucleoli. However, 1 or more of these 4 characteristic morphological features such as 3-dimensional cluster with cell disorientation, isolated malignant cells, irregular nuclear contour/nuclear grooves/notches (<under>></under>5% atypical cell population), and marked nuclear size variation 1:4 or higher was mainly present in adenocarcinoma. Conclusions: A combination of at least 2 of these 4 characteristic cytomorphological features needs to be present before rendering an unequivocal diagnosis of adenocarcinoma. Using these strict cytological criteria would have eliminated these false-positive diagnoses.