RET and medullary thyroid gland carcinoma: MTC originates as a sporadic (75–80%) malignancy or a manifestation of hereditary syndromes (20–25%), i.e., multiple endocrine neoplasia type 2 (MEN2A or MEN2B)/familial MTC, with an autosomal dominant pattern due to germline mutations of the RET gene (Pacini et al., 2010).