Fine-needle aspiration cytology of islet cell tumors.

Islet cell tumors of the pancreas are neuroendocrine neoplasms whose biologic behavior has been well characterized. Frequently, these tumors produce one or more hormones which may strongly affect the patients' clinical presentation. In this study, we have examined fine-needle aspirates (FNA) from 13 islet cell tumors and have summarized their cytomorphologic appearances. The smears prepared from aspirates of the islet cell tumors displayed loose cellular arrangements and numerous single cells, with most cases demonstrating a predominance of single cells over the loose groups. An important diagnostic feature was the uniform appearance of the neoplastic cells. Nuclei were small to moderate in size, always round to oval in shape, and frequently contained small nucleoli. In 11 cases, the nuclear chromatin pattern was finely granular and evenly-distributed while in two cases the chromatin was coarser. Eccentrically located nuclei were commonly found and binucleated cells were seen in one-half of the aspirates. At least a moderate amount of finely granular cytoplasm was always identifiable. Immunocytochemical stains for neuron-specific enolase were positive in all five of our cases in which staining for this marker was attempted and chromogranin was positive in five of six cases. Generally, our cytomorphologic observations were supported by the findings of other investigators as reported in the cytology literature. The cytomorphologic characteristics of islet cell tumors are distinctive, and appropriate ancillary studies can be used to support the FNA diagnosis of this entity.