RET and medullary thyroid gland carcinoma: However, in the LIBRETTO-001 trial (ClinicalTrials.gov no. NCT03157128), evaluating toxicity and efficacy of selpercatinib in patients affected by RET-mutated MTC with and without previous vandetanib or cabozantinib treatment, cough and dyspnea were reported in 18% and 16%, respectively (17).