RET and medullary thyroid gland carcinoma: Unlike other RET inhibitors, this drug presents a rigid macrocyclic structure which makes it active against various mutations, including the solvent front mutation (SFM) RET G810 that conveys resistance to other selective RET inhibitors but not the gatekeeper V804, which limits its effectiveness in some patients with MTC especially whose disease harbor both gatekeeper and SFMs [7•].