RET and medullary thyroid gland carcinoma: The screening of RET mutations has been carried out in different series of sporadic MTC, however the observed frequencies are variable (12–100%) (Hofstra et al, 1994; Zedenius et al, 1994; Jhiang et al, 1996; Marsh et al, 1996, 2003; Romei et al, 1996; Wohllk et al, 1996; Bugalho et al, 1997; Scurini et al, 1998; Shan et al, 1998; Uchino et al, 1998, 1999; Bockhorn et al, 1999; Dvorakova et al, 2008; Elisei et al, 2008).