FGFR Testing in Metastatic Urothelial Carcinoma—Who, When, and How to Test

Metastatic urothelial carcinoma (mUC) is a lethal cancer with limited therapeutic options. Advances in genomic and transcriptomic research have deepened the understanding of mUC biology, leading to the identification of clinically relevant molecular alterations that represent potential actionable targets. This has broadened the treatment landscape of the disease to include novel agents, such as antibody–drug conjugates (e.g., enfortumab vedotin) and targeted therapies, including the pan-fibroblast growth factor receptor (FGFR) inhibitor erdafitinib. Genomic alterations in FGFR3 are well-established oncogenic drivers in bladder cancer and represent predictive biomarkers of response to FGFR-targeted therapies. The phase III THOR trial demonstrated the clinical benefit of erdafitinib in previously treated mUC patients harboring FGFR3 alterations and supported its subsequent approval by the European Medicines Agency. In this context, accurate molecular profiling is essential to guide patient selection for FGFR inhibitor therapy. Equally important is the standardization and timely implementation of FGFR3 testing in clinical practice to optimize treatment planning. This review addresses key considerations in FGFR3 testing in mUC and discusses how it can be routinely incorporated into clinical practice.