Neuroendocrine Neoplasms

Abstract

The subject of neuroendocrine neoplasms, starting with the definition of what neuroendocrine means, may be thoroughly confusing to the beginner. Although these tumors are mentioned in many other chapters in this book, this chapter will focus on the general concepts and definitions pertaining to this subject. Morphologically, there is no single feature that defines neuroendocrine neoplasms as a group. Instead, neuroendocrine morphology is defined by a constellation of several cytologic and architectural features. When someone says a tumor “looks neuroendocrine,” they are implying these features. One of the challenges with neuroendocrine tumors is that this family includes tumors with quite different morphology and behavior, spanning from well-differentiated tumors (such as lung carcinoids) to highly aggressive, poorly differentiated carcinomas (such as small cell carcinoma). Whereas the defining neuroendocrine features are usually very obvious in well-differentiated neoplasms, they may be quite subtle to barely detectable in poorly differentiated carcinomas. Nevertheless, even in the latter tumors, the overall uniformity and dispersed finely granular chromatin should be preserved, and at least a hint of neuroendocrine architecture (in the form of nesting, rosettes, or ribbons) is usually present.