Pancreatic neuroendocrine tumor: a diagnostic challenge in fine needle aspiration cytology

Abstract

Background: Pancreatic neuroendocrine tumors (PNETs) are unusual neoplasms, constituting 1–2% of pancreatic tumors. They have varied clinical presentations which make them challenging to diagnose at an early stage. Here we present a misdiagnosed PNET. Methods: A 43-year-old Caucasian male with a history of fever and weakness associated with hypercalcemia was evaluated for a pancreatic mass. CT showed an irregular heterogeneous mass (13.2 cm × 11.9 cm) in the abdomen with the epicenter of the mass in the pancreatic tail with invasion into the spleen and gastric fundus. He also had multiple enhancing lesions in the liver. Results: Fine needle aspirate cytology (FNAC) of the first biopsy showed crowded groups of malignant cells in a bloody background. Immunohistochemistry (IHC) stains for further characterization were attempted but non-contributory due to pauci-cellularity and the patient was diagnosed with pancreatic adenocarcinoma based on the available information. He was started on cytotoxic chemotherapy for a pancreatic adenocarcinoma. He had stable disease on scans for approximately 9 months at which time, on surveillance imaging, a radiologist suggested another FNAC as the stability and arterial enhancement on CT suggested a PNET. The second FNAC was diagnostic of a PNET, grade 2 based on IHC stains positive for CD56, Ki67 (15%) and strongly positive synaptophysin/chromogranin. Conclusion: This case highlights the problems in an accurate diagnosis of PNET using FNAC and underlines the significance of keeping this entity in the differential diagnosis. The histology and natural history of a PNET is markedly different from a pancreatic adenocarcinoma. With an initial diagnosis of a pancreatic malignancy on FNAC, it is vital to differentiate it from the more common pancreatic adenocarcinoma to the rare PNET.