Multiple endocrine neoplasia type 2B (MEN2B) is a rare genetic disorder characterized by the development of tumors in multiple endocrine glands, including the thyroid, adrenal, and parathyroid glands. It is caused by mutations in the RET gene and is associated with an increased risk of medullary thyroid carcinoma and pheochromocytoma (a typically benign adrenal gland tumor).