Neuroendocrine Neoplasms of the Lung

In this review, we discuss the clinical and pathologic aspects of epithelial neuroendocrine neoplasms of the lung and compare the current classification with that of gastrointestinal (GI) neuroendocrine neoplasms. Endocrine neoplasms can be broken down into 2 major categories, which, as currently believed, are not part of a continuum, but rather distinct pathogenetic entities. Well-differentiated neuroendocrine tumors (NETs) are low-grade malignancies. In the lung, the term “carcinoid” is still applied for these, which are classified as typical or atypical. In the pancreas and GI tract, well-differentiated NETs are graded based on Ki-67 proliferative index into 3 numeric categories. Poorly differentiated neuroendocrine carcinomas (NECs) are classified in both organ systems into small cell carcinoma and large cell NEC. In this review, “NET” is used interchangeably with “well-differentiated NET.” Although often used in the GI tract, “poorly differentiated NEC” is not a term used in the lung, where the distinction between small cell carcinoma and LCNEC is more clear-cut than in the GI tract.