RET and medullary thyroid gland carcinoma: The evolving understanding of disease-specific molecular therapeutic targets has led to the approval of several multi-tyrosine kinase inhibitors (multi-TKIs) for RAI refractory DTC such as Sorafenib (VEGFR/PDGFR and Raf), and Lenvatinib (VEGFR/PDGFR/FGFR/RET), and for MTC such as Vandetanib (EGFR/VEGFR/RET inhibitor) and Cabozantinib (VEGFR/RET) [125,126] (Figure 5).