Brush cytology of acinar cell carcinoma of the pancreas with intraductal growth: a case report.

We describe a rare case of pancreatic acinar cell carcinoma (ACC) with intraductal growth in a 77-year-old man, which was diagnosed by endoscopic brush cytology. Preoperative imaging revealed an ill-defined mass involving the main pancreatic duct of the body, which was suspected to be an invasive ductal carcinoma. Endoscopic brush cytology showed several thick, small to large clusters of tumor cells. However, a loosely cohesive or individual cell arrangement was more prominent. Singly dispersed naked nuclei, occasionally with crush artifact, were frequently observed. The nuclear contour was smooth and chromatin was finely clumped. The cytoplasm contained many coarse D-PAS-positive granules. Histologically, the tumor expansively invaded to parenchyma and expanded to fill the pancreatic ducts. Ultrastructurally, the tumor cells were less cohesive with scarce tight junctions, and their cytoplasm contained numerous zymogen granules and filamentous inclusions. Although ACCs usually show expansive growth, the incidence of intraductal extension may be higher than previously considered. A few of the characteristic cytomorphological features described here may be useful for differential diagnosis of this tumor from malignant epithelioid neoplasms involving the large pancreatic ducts.