Erdafitinib is primarily used in the treatment of advanced or metastatic urothelial carcinoma, specifically in patients with specific genetic mutations in the FGFR3 or FGFR2 genes. These mutations can lead to abnormal cell growth and cancer progression. The drug works by inhibiting fibroblast growth factor receptors (FGFRs), which play a key role in cell proliferation, survival, and differentiation. By targeting these receptors, erdafitinib helps to slow down or stop the growth of cancer cells. It is typically prescribed for patients who have previously undergone platinum-containing chemotherapy and have experienced disease progression. The use of erdafitinib is often guided by genetic testing to identify patients who are most likely to benefit from this targeted therapy.