RET and medullary thyroid gland carcinoma: MEN2 is a hereditary disease resulting from mutations of the RET protooncogene subclassified into MEN2A (MTC, pheochromocytoma, and primary hyperparathyroidism) and MEN2B (MTC, pheochromocytoma, Marfanoid habitus, mucous neuromas, and intestinal ganglioneuromatosis).