RET and multiple endocrine neoplasia type 2A: Multiple endocrine neoplasia type 2 (MEN2) is composed of three clinical subtypes, multiple endocrine neoplasia type 2A (MEN2A), familial medullary thyroid carcinoma, and multiple endocrine neoplasia type 2B, all of which are associated with germline mutations in the RET proto-oncogene.