Commonest thyroid tumor in MEN (multiple endocrine neoplasia)

Medullary Thyroid Carcinoma Medullary carcinoma is a less frequent type derived from parafollicular or C-cells present in the thyroid and comprises about 5% of thyroid carcinomas. It is equally common in men and women. There are 3 distinctive features which distinguish medullary carcinoma from the other thyroid carcinomas. They are : its familial occurrence, secretion of calcitonin and other peptides, and amyloid stroma. 1. Familial occurrence. Most cases of medullary carcinoma occur sporadically, but about 10% have a genetic background with point mutation in RET-protooncogene located on chromosome 10q. The familial form of medullary carcinoma in association with pheochromocytoma and parathyroid adenoma (multiple endocrine neoplasias, MEN II A), or with pheochromocytoma and multiple mucosal neuromas (MEN II B). 2. Secretion of calcitonin and other peptides. Like normal C-cells, tumour cells of medullary carcinoma secrete calcitonin, the hypocalcaemic hormone. In addition, the tumour may also elaborate prostaglandins, histaminase, somatostatin, vasoactive intestinal peptide (VIP) and ACTH. These hormone elaborations are responsible for a number of clinical syndromes such as carcinoid syndrome, Cushing's syndrome and diarrhoea. 3. Amyloid stroma. Most medullary carcinomas have amyloid deposits in the stroma which stains positively with usual amyloid stains such as Congo red. The amyloid deposits are believed to represent stored calcitonin derived from neoplastic C-cells in the form of prohormone. Most cases of medullary carcinoma present as solitary thyroid nodule but sometimes an enlarged cervical lymph node may be the first manifestation. Most medullary carcinomas are slow-growing. Regional lymph node metastases may occur but distant organ metastases are infrequent. The prognosis is better in familial form than in the sporadic form: overall 10-year survival rate is 60-70%. Ref: TEXTBOOK OF PATHOLOGY 6th EDITION - HARSH MOHAN PAGE NO:813-814