The neuroendocrine carcinoma arising from parafollicular 'C' cells of thyroid is:

MEDULLARY CARCINOMA OF THE THYROID (MCT) These tumours arise from parafollicular ‘C’ cells which are derived from ultimobranchial bodies and not from thyroid foillicle. These tumours present in two different ways. Sporadic is common, seen in about 80-90% of cases. Familial variety present as a part of multiple endocrine neoplasia (MEN). MEN Type I Pituitary adenoma Parathyroid adenoma Pancreatic adenoma MEN Type IIa Parathyroid adenoma Phaeochromocytoma Medullary carcinoma of thyroid When it is associated with mucocutaneous neuromas involving lips, tongue, eyelids, it is called Sipple syndrome, with an occasional marfanoid habitus (MEN type IIb) It has got a characteristic amyloid stroma  These tumours are not TSH-dependent and do not take up radioactive iodine  Hormones produced by MCT Calcitonin  Prostaglandins Serotonin (5-HT), ACTH Spread Both by lymphatics and blood, thus, worsening the prognosis. Key Concept: Medullary Carcinoma arises from parafollicular C cells which are derived from ultimobranchial bodies and not from thyroid follicle. The medullary carcinoma produces hormones such as Calcitonin, Prostaglandins and serotonin. Reference:  Manipal Manual of Surgery 4th ed page no 348