Histologic appearance of the spectrum of neuroendocrine tumors arising in the gastrointestinal tract

Examples of neuroendocrine tumors. Well-differentiated neuroendocrine tumor shows an organoid pattern and difficult-to-find mitotic activity on hematoxylin and eosin (H&E) stain (A), and the proliferative rate (as measured by the Ki-67 labeling index) is very low (<1% in this case) (C). By contrast, poorly differentiated neuroendocrine carcinoma shows frank features of carcinoma with numerous mitotic figures and tumor necrosis on H&E stain (B), and the Ki-67 labeling index is very high (>80% in this case) (D). (200x original magnification.)