Medullary Ca of thyroid are neuroendocrine neoplasms derived from the calcitonin-secreting parafollicular cells (C cells) of the thyroid which in turn are derived from the ultimobranchial bodies (These C cells are concentrated supernaturally in the thyroid lobes, which is where MTC usually develops) Most MTCs (75-80%) arise sporadically. The remainder occurs in the setting of MEN syndromes 2A or 2B or as familial tumors without an associated MEN syndrome. The sporadic MTCs tend to originate in one lobe, whereas bilaterality and multicentricity are common in familial cases. The familial cases are also associated with C-cell hyperplasia, which is considered premalignant lesion of MTC. Familial cases occur at a younger age, even childhood. Sporadic cases are seen in the 6th decade. RET proto-oncogenes are known to play an impoant role in the development of both familial & sporadic MTCs. Patients with MTC often present with a neck mass that may be associated with palpable cervical lymphadenopathy (early spread to lymphatics is common) Diarrhoea is a feature in 30% of cases and this may be due to 5-hydroxytryptamine or prostaglandins produced by the tumour cells. (Re B & L 25/e p797) Distal blood-borne metastasis to the liver, bone (frequently osteoblastic), and lung occur late in the disease. Diagnosis is established by FNAC - the presence of amyloid stroma is diagnostic. raised serum calcitonin and CEA levels (Calcitonin is a more sensitive tumor marker, but CEA is a better predictor of prognosis) As it is not possible to distinguish sporadic from the familial disease at initial presentation, all new patients with MTC should be screened for RET point mutations pheochromocytoma (24 hr urinary levels of VMA, catecholamine & metanephrine) hyperparathyroidism (serum calcium) (It is impoant to rule out a coexisting pheochromocytoma to avoid precipitating a hypeensive crisis & death during surgery) Also, remember MTC tumors don't take up radioiodine and are not hormone dependent. Ref : Schwaz Sx 9/e p1367