Up to 7% cases of apparently sporadic isolated MTC have germline MEN2A RET pathogenic variants, predominantly non-cysteine variants, e.g., V804M, with a moderate MTC risk (Romei et al. 2011), whereas ∼55% of sporadic MTC cases have a somatic RET variant (Fig. 2) (Ciampi et al. 2019). Here, RET is linked to medullary thyroid gland carcinoma.