NR4A1 and breast cancer: Selpercatinib is a first-in-class selective RET inhibitor that recently received US FDA approval for the treatment of metastatic RET fusion–positive non–small-cell lung cancer and advanced or metastatic RET-altered thyroid cancers.9-11 However, for patients with RET fusion–positive breast cancer, standard of care is currently limited to hormonal therapy, chemotherapy, and anti-HER2–targeted therapies based on hormone receptor and HER2 status.