<prompt> Medullary carcinoma of thyroid is associated with mutation inRETRASNFRb  <response>: Ref Robbins 8e p1124_1126,9e p284 Medullary thyroid cancer is a form of thyroid carcinoma which originates from the parafollicular cells C cells, which produce the hormone calcitonin. Medullary tumors are the third most common of all thyroid cancers and together make up about 3 of all thyroid cancer cases.2 Approximately 25 of medullary thyroid cancer cases are genetic in nature, caused by a mutation in the RET proto-oncogene. This form is identified as familial medullary thyroid cancer FMTC. When MTC occurs by itself it is termed sporadic medullary thyroid cancer SMTC. When it coexists with tumors of the parathyroid gland and medullary component of the adrenal glands pheochromocytoma it is called multiple endocrine neoplasia type 2 