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

## TL;DR

This paper explains how and why FGFR3 testing should be used in bladder cancer to guide targeted treatments and improve patient outcomes.

## Contribution

The paper provides practical guidance on implementing FGFR3 testing in clinical practice for metastatic urothelial carcinoma.

## Key findings

- FGFR3 alterations are predictive biomarkers for response to FGFR-targeted therapies like erdafitinib.
- The THOR trial confirmed clinical benefits of erdafitinib in patients with FGFR3-altered metastatic urothelial carcinoma.
- Standardized FGFR3 testing is essential for selecting appropriate patients for targeted therapy.

## Abstract

Bladder cancer that has spread to other parts of the body-called metastatic urothelial carcinoma (mUC)-is an aggressive disease with few effective treatments. Recent genetic research has revealed important changes in tumor DNA and gene activity that can represent targets for use of more precise treatments. One of these targets is a gene called FGFR3, which, when altered, can drive cancer growth. New drugs that specifically block this pathway, such as erdafitinib, have shown real benefits for patients whose tumors carry these FGFR3 changes, as confirmed in a large international study (the THOR trial). Because of this, testing for FGFR3 alterations has become an important step in deciding which patients might benefit from these treatments. This article aims to explain why and how FGFR3 testing should be performed in everyday clinical practice, helping doctors select the right therapy for each patient. The findings could guide cancer centers on how to implement these tests more consistently and effectively, improving outcomes and advancing precision medicine in bladder cancer care.

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.