RET and medullary thyroid gland carcinoma: The “Phase 1/2 Study of Oral LOXO-292 in Patients With Advanced Solid Tumors, Including RET Fusion-Positive Solid Tumors, Medullary Thyroid Cancer, and Other Tumors With RET Activation” LIBRETTO-001 trial is an open-label, first-in-human study that was designed to evaluate the safety, tolerability, pharmacokinetic, and preliminary antitumor activity of selpercatinib (LOXO-292), an oral RET kinase inhibitor, in advanced refractory solid tumor patients, including RET fusion-positive mCRC (NCT 03157128).