FDA-approved RET protein-tyrosine kinase inhibitors in the management of RET-driven thyroid and lung cancer.

RET is a transmembrane receptor protein-tyrosine kinase that is required for the (i) survival and maturation of the enteric nervous system, the autonomic nervous system, and sensory neurons, (ii) renal development, and (iii) spermatogenesis. RET activation by its glial-cell derived neurotrophic factor (GDNF) ligands differs from that of all other receptor protein-tyrosine kinases because of the requirement for additional GDNF family receptor-α co-receptors (GFRα1/2/3/4, GFRAL). Activating RET-point mutations occur in multiple endocrine neoplasia syndromes (MEN2A, MEN2B) and in isolated medullary thyroid cancer. RET-fusion proteins, commonly KIF5B-RET, occur in NSCLC. More than three dozen fusion partners of RET have been described in papillary thyroid cancer. Several multikinase blockers targeting RET have been approved by the FDA for the treatment of cancer: (i) vandetanib for medullary thyroid carcinoma and (ii) cabozantinib, lenvatinib, and sorafenib for differentiated thyroid cancer. Pralsetinib is a specific RET blocker that is FDA-approved for the treatment of medullary thyroid cancer, RET-fusion positive thyroid cancer and NSCLC. Selpercatinib is FDA-approved for the management of RET-mutant medullary thyroid cancer, RET-fusion-positive thyroid cancer, and other RET-fusion-positive solid tumors. The RET signaling pathway participates in the pathogenesis of cancer, particularly in thyroid and lung cancer. Currently, the number of new cases of thyroid cancer bearing RET mutations or RET-fusion proteins is about 13,000 per year and the number of cases of RET-driven NSCLC range from about 2000-4000 per year in the United States. Inactivating RET mutations result in Hirschsprung disease, a congenital disorder leading to aganglionosis of the gastrointestinal tract.