The tumor is composed of solid sheets of epithelioid and spindle cells separated by delicate fibrovascular stroma. Amyloid deposition is not seen in this field. The cytoplasm is amphophilic. The nuclei are round or oval with finely granular chromatin and have small punctate nucleoli. Immunohistochemistry should be performed to confirm the diagnosis of medullary thyroid carcinoma. The usual profile is as follows: POSITIVE - cytokeratin, TTF-1, calcitonin, neuroendocrine markers (Chromogranin, NSE, synaptophysin), and CEA. NEGATIVE - thyrogrobulin.