Neuroendocrine Carcinoma : Microscopic
Neuroendocrine Carcinomas of the GI Tract - Microscopic Features: The tumor cells may be arranged in nests, ribbons, trabecular, gyriform, and solid growth patterns. There is marked cytologic atypia, necrosis, angiolymphatic invasion, and frequent invasion of overlying mucosa with ulceration. The defining characteristic is mitotic rate >20/10 HPFs and/or Ki-67 labeling index >20%. This category includes large cell neuroendocrine carcinoma with a more organoid appearance (less frequent) as well as small cell carcinoma (more common) with typical histology resembling those seen in the lung. Foci of glandular or squamous differentiation may be present.