Selpercatinib (SEL) is a selective RET (rearranged during transfection) inhibitor that has a good safety profile and potent antitumor effects against RET mutation-positive medullary thyroid carcinoma and RET fusion gene-positive thyroid carcinoma, as demonstrated by the LIBRETTO-001 trial. This evidence concerns the gene RET and medullary thyroid gland carcinoma.