FGFR-Altered Urothelial Carcinoma: Resistance Mechanisms and Therapeutic Strategies.

Fibroblast growth factor receptor (FGFR) 2/3 alterations have been implicated in tumorigenesis in several malignancies, including urothelial carcinoma. Several FGFR inhibitors have been studied or are in development, and erdafitinib is the sole inhibitor to achieve regulatory approval. Given the rapidly evolving treatment landscape for advanced urothelial carcinoma, including regulatory approvals and withdrawals, determining the most appropriate treatment strategies and sequencing for FGFR-altered urothelial carcinoma is becoming increasing critical. However, the clinical efficacy of FGFR inhibitors is limited by acquired resistance similar to that seen with other tyrosine kinase inhibitors. Additional challenges to the clinical use of FGFR inhibitors include treatment-related adverse events and the financial costs associated with treatment. In this review, we describe known mechanisms of FGFR inhibitor resistance, including gatekeeper mutations, domain mutations, and the development of new mutations. In addition, we discuss management strategies, including ongoing clinical trials evaluating FGFR inhibitors, antibody-drug conjugates, and combination therapies with immune checkpoint inhibitors that may provide additional treatment options for localized and metastatic urothelial carcinoma.