Report of a case of acinar cell carcinoma with its differential diagnosis on endoscopic ultrasound-guided fine-needle aspiration cytology

Acinar cell carcinomas (ACCs) of the pancreas are a rare tumor accounting for only about 2% of all pancreas tumors. We report herein on this case and discuss how to distinguish ACCs from neuroendocrine tumors (NETs) and solid pseudo-papillary tumor (SPTs) morphologically and immunohistochemically. In cytological findings, the nuclear-cytoplasmic ratio was high, and the cytoplasm was granular, but zymogen granules were not evident. The nucleus was biased in location, assuming small circular and irregular forms. Chromatin was fine granular in shape and distributed nonuniformly, accompanied by evident nucleoli. Immunohistochemically was positive for β-catenin (cell membrane and part of nuclei), synaptophysin (focal), chromogranin A (focal) and chymotrypsin were all positive. Although the cytological distinction of ACCs from NETs and SPTs is difficult, the nuclear chromatin pattern and nuclear inclusion bodies, pseudopapillary arrangement and hyaline globules seem to play an important role in the cytological differential diagnosis. Furthermore, not only enzymatic and neuroendocrine markers, but also antibodies to β-catenin, vimentin and so on seem to be useful in the differential diagnosis.