The cut surfaces are usually firm and grey. Nuclei are round to ovoid with finely-dispersed chromatin. Nucleoli are small. Mitoses are usually fewer than 1-2 per high power field. A characteristic feature is the detachment of some nests from the adjacent stroma.
Tumor grows in sheets interspersed with thin-walled vessels.
Tumors react with antibodies to cytokeratin and chromogranin A, as well as other neuroendocrine markers including synaptophysin and Leu-7. Additionally, tumors may show reactivity for ACTH, serotonin, calcitonin, gastrin, cholecystokinin, or somatostatin, even if there is no clinical evidence of their presence. Parathyroid tumors can be distinguished by their staining with antibody to parathormone. Paragangliomas express neuroendocrine markers but do not react with cytokeratin. Response to chemotherapy or radiation alone is poor.