MTC is sporadic in origin in 60 to 75 % of all patients with MTC, while the others exhibit germline mutations in the RET proto-oncogene, namely patients with multiple endocrine neoplasia type 2A (MEN2A), multiple endocrine neoplasia type 2B (MEN2B), and familial MTC syndrome (FMTC). This evidence concerns the gene RET and multiple endocrine neoplasia type 2B.