RET and medullary thyroid gland carcinoma: Multiple Endocrine Neoplasia type 2B (MEN2B) is an autosomal dominant cancer syndrome caused by a mutation in rearranged during transfection (RET) proto-oncogene and includes medullary thyroid carcinoma, pheochromocytoma, gastrointestinal neuromas, and mucosal ganglioneuromas.