Moreover, the hinge region of the FGFR4 complex has a unique non-conserved Cys552 structure, whereas the corresponding positions of FGFR1-3 are tyrosine, providing feasibility for the development of selective covalent FGFR4 inhibitors.109 Pan-FGFR inhibitors that have been approved by the FDA are erdafitinib, pemigatinib, and infigratinib for indications including uroepithelial cancers, bile duct cancers, or myeloid/lymphoid neoplasms.110,111 Compared to these pan-FGFR inhibitors, selective FGFR4 inhibitors have better manageable toxicity. The gene discussed is FGFR4; the disease is bile duct cancer.