Around 25% of the MTC cases are hereditary due to germline mutations on chromosome 10, activating the REarranged during Transfection (RET) proto-oncogene.1 These mutations are inherited in an autosomal dominant pattern and cause the endocrine syndromes multiple endocrine neoplasia (MEN) type 2A and MEN type 2B. This evidence concerns the gene RET and multiple endocrine neoplasia type 2B.