Histopathologic Diagnosis of Neuroendocrine Neoplasms of Head and Neck, Lung and Gastrointestinal Tract

Abstract

Neuroendocrine neoplasms are classified as epithelial and non-epithelial based on their origin being from epithelial neuroendocrine progenitor cells or derived from the neural crest. The latter are negative for cytokeratin (hence non-epithelial) and mostly result from neoplastic transformation of paraganglia. Here, we are reviewing the most important histologic and immunophenotypic characteristics of neuroendocrine carcinomas as well as the current WHO classification guidelines. The terminology of neuroendocrine neoplasms is confusing due to various classification systems employed for each internal organ. In the lung and GI tract, for example, “neuroendocrine tumors” comprise carcinomas of different degree of differentiation and histologic grade. While in the lung the term refers strictly to low-grade neuroendocrine carcinomas, in the GI tract it comprises both low- and high-grade neuroendocrine carcinomas. Despite concerted efforts to unify the overall classification of neuroendocrine carcinomas across organs, major differences continue to persist.