Histologic Features: Microscopically, thymic carcinoids are composed of a uniform population of polygonal tumor cells with small round regular nuclei, finely granular chromatin and pale eosinophilic cytoplasm. By definition, there is no necrosis and mitotic activity is low. The tumor cells form trabeculae, rosettes, festoons, solid nests, and glandular structures. There is a delicate vascular stroma between the trabeculae and nests. Several rosettes can be seen in this field.