Fine needle aspiration cytology of neuroendocrine tumors of the pancreas. A cytologic, immunocytochemical and electron microscopic study.

We report the fine needle aspiration cytology findings in six cases of neuroendocrine tumor of the pancreas. Three cases were from the pancreas, two from hepatic metastases and one from a peripancreatic lymph node metastasis. The cytologic features that permitted a preoperative diagnosis of pancreatic neuroendocrine tumor were: a cellular aspirate; numerous isolated cells and irregular, loose, dyshesive cellular aggregates; minimal nuclear pleomorphism; infrequent mitoses; fine, evenly dispersed nuclear chromatin with occasional inconspicuous nucleoli; a scant-moderate amount of granular, amphophilic, well-defined cytoplasm; clustering of tumor cells around segments of capillaries; and rosette formation. The differential diagnosis includes cells derived from normal pancreatic acini, islet cell hyperplasia, acinic cell carcinoma, well-differentiated pancreatic adenocarcinoma, metastatic small cell undifferentiated carcinoma of the lung, pancreatic small cell anaplastic carcinoma and malignant lymphoma. The application of immunocytochemistry to cytologic smears can be easily and reliably performed to confirm the neuroendocrine nature of the tumor and identify the specific type of polypeptide hormone or hormones produced by these tumors. Four aspirates showed immunoreactivity for chromogranin, and one was positive for gastrin. Cells of a lipid-rich neuroendocrine tumor were negative for chromogranin; however, the tissue section contained neuron specific enolase, and neurosecretory granules were demonstrated by electron microscopy.