RET and medullary thyroid gland carcinoma: The hereditary form accounts for about 25% of all MTC, shows a genotype–phenotype correlation and is due to RET (REarranged during Transfection) oncogene mutations, with the autosomal-dominant transmission, associated with hereditary multiple endocrine neoplasia syndrome (MEN) type 2A and 2B or the related familial MTC syndrome (FMTC).