Acinar Cell Carcinoma of the Pancreas

Abstract

Acinar carcinoma is extremely rare. In this report, we present the clinical and pathologic features of three cases that we have encountered in a busy EUS-FNA service. All 3 cases were diagnosed on final histology using immunostains and electron microscopy. Our cases demonstrated the rarity of this neoplasm and the need for ancillary testing for accurate diagnosis.A cinar cell carcinoma (ACC) is a rare carcinoma of the exocrine pancreas, accounting for approximately 1% to 2% of all pancreatic neoplasms in adults. 1 The diagnosis of ACC often relies on the cytology specimen that is obtained during endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA). Cytologically, the preoperative diagnosis relies on evidence of acinar differentiation, which can be challenging because of the morphologic overlap with other neoplasms; therefore, final diagnosis often depends on ancillary techniques, such as immunohistochemistry. 2 We reviewed all of our cytology records, from 2000 to 2013, searching for ACC diagnosed on cytology or histology. All cases with a diagnosis of ACC on final histology were included, regardless of the preoperative cytology diagnosis. We identified 3 patients who had histologically confirmed ACC with accompanying cytology. CASE 1 Case HistoryAn 87-year-old man with a history of prostate cancer presented with an incidental 4-cm uncinated mass in the pancreas. The patient had EUS-FNA performed, and the rapid on-site diagnosis was epithelial neoplasm and necrosis. The cell block was insufficient for further workup. The final diagnosis included a differential diagnosis of neuroendocrine neoplasm, ductal carcinoma, metastatic prostate carcinoma, and solid pseudopapillary neoplasm (SPN).Cytology showed moderate cellularity; tumor cells were arranged in moderately sized clusters with single naked nuclei in the background with necrosis. The nuclear membranes were smooth with mild anisonucleosis and occasional rosetting of tumor cells (Fig. 1).The pancreatic lesion was resected and on histology showed extensive necrosis with large nests of malignant cells. The cells were arranged as trabecular forms, rosettes, and some solid areas. The nuclei were pleomorphic with numerous prominent nucleoli and slightly irregular nuclear membranes. There was abundant eosinophilic granular cytoplasm. The tumor was positive for periodic acid-Schiff without diastase (PAS-D) and negative for chromogranin and synapthophysin. The final diagnosis was ACC. Immunohistochemistry was performed and showed cytoplasmic staining for trypsin and chymotrypsin confirming the acinar origin of the neoplasm. In addition, ultrastructure analysis showed electron-dense granules measuring 400 to 800 nm in diameter. The granules were variable in size, and there were no neurosecretrory granules identified (Fig. 2). CASE 2An 81-year-old woman presented with weight loss and abdominal pain. No discrete mass was visualized on computed tomography; however, on EUS, a 2-cm mass was seen in the head of the pancreas. The patient underwent EUS-FNA, and the mas...