Old, New, and Emerging Immunohistochemical Markers in Pheochromocytoma and Paraganglioma.

The evolution of genetic research over the past two decades has greatly improved the understanding of pheochromocytomas and paragangliomas. It is now accepted that more than one third of pheochromocytoma and paragangliomas arise in the context of syndromic disease, usually hereditary. The genetic profile of these tumors also has important prognostic implications which may help guide treatment. Accompanying the changing molecular landscape is the development of new immunohistochemical markers. Initially used in assisting with diagnosis, immunohistochemical markers have now become an important adjunct to screening programs for inherited conditions and subsequently as prognostic markers. The accessibility and efficiency of immunohistochemistry bring pathologists to the forefront in triaging patients based on tumor genotype-phenotype. In this review, we provide an update on the role of immunohistochemistry in the diagnosis of pheochromocytomas and paragangliomas, as an adjunct to assessment for hereditary disease and finally as a potential tool to assist risk stratification.