Hereditary medullary thyroid carcinoma (MTC) is a manifestation of multiple endocrine neoplasia (MEN) type 2A and MEN 2B syndromes caused by germline, activating mutations in the RET (REarranged during Transfection) proto-oncogene (10q11.2). This evidence concerns the gene RET and multiple endocrine neoplasia type 2A.