Many bladder cancers that are resistant to chemotherapy and immunotherapy have mutations in the gene encoding a growth protein called fibroblast growth factor receptor (FGFR). Erdafitinib is a inhibitor of this FGFR growth protein and was studied in metastatic bladder cancer with FGFR mutations. In a trial of patients with these mutations, about 40% had a significant shrinkage of their tumor with this treatment. Main side effects include gastrointestinal issue, electrolyte imbalances and weakness. In 2019, the FDA approved this drug for patients with locally advance or metastatic urothelial carcinoma which has susceptible fibroblast growth factor receptor genetic alterations who have progressed during or following at least one line of prior platinum-containing chemotherapy.