Adrenal and extra-adrenal nonfunctioning composite pheochromocytoma/paraganglioma with immunohistochemical ectopic hormone expression: comparison of two cases.

Adrenal composite pheochromocytoma is rare, most of which is functional, and extra-adrenal composite paraganglioma is extremely rare. We describe and compare the clinicopathological and immunohistochemical features of a retroperitoneal extra-adrenal composite paraganglioma and an adrenal composite pheochromocytoma. Both tumors were nonfunctioning and laboratory tests revealed no biochemical abnormalities. Both tumors were composed of typical paraganglioma/pheochromocytoma closely admixed with ganglioneuroma component. In addition to typical immunohistochemical phenotypes characteristic of each component, both tumors showed focal staining of somatostatin, and the adrenal tumor was also regionally positive for insulin and prolactin. Despite this aberrant immunohistochemical expression, relevant clinical symptoms or laboratory abnormalities were absent. These tumors serve to exemplify the extremely rare occurrences of clinically silent, nonfunctioning composite pheochromocytoma or paraganglioma with aberrant expression of hormones.