A germ-line activating mutation in the RET (REarranged during Transfection) protooncogene is reported in nearly all cases of hereditary forms of MTC associated with multiple endocrine neoplasia type 2 (MEN 2), and a somatic RET mutation can be present in up to 50% of sporadic forms of MTC [3, 4]. The gene discussed is RET; the disease is multiple endocrine neoplasia type 2.