RET and multiple endocrine neoplasia type 2: Multiple endocrine neoplasia type 2 (MEN2) occurs due to activating mutations in the RET proto-oncogene. Medullary carcinoma of the thyroid and pheochromocytomas are common in both MEN2A and MEN2B. In addition, parathyroid adenomas are common in MEN2A (10-15%), and mucosal neuromas are common in MEN2B [12].