RET and medullary thyroid gland carcinoma: Approximately 20% of cases are familial, secondary to a germline rearranged during transfection (RET) mutation, while the remaining 80% are sporadic (Bai et al. 2020) and also harbour a somatic RET mutation in more than half of all cases, with RET M918T being the most frequent genetic alteration encountered in 30–50% of aggressive sporadic MTC (Dvorakova et al. 2008, Taccaliti et al. 2011).