biomarkersBiomarker

FGFR3 alteration (mutation or fusion)

aka FGFR3 mutation, FGFR3 fusion, FGFR3-TACC3, FGFR3::TACC3, FGFR3 S249C, FGFR3 R248C, FGFR3 Y373C, susceptible FGFR3 genetic alterations, FGFR alteration bladder

FGFR3 point mutations and TACC3 fusions drive about 15 to 20 percent of advanced bladder cancers. Erdafitinib is approved for tumours with these 'susceptible' alterations after one prior treatment.

The erdafitinib (Balversa) label covers locally advanced or metastatic urothelial carcinoma with susceptible FGFR3 genetic alterations after at least one line of systemic therapy (THOR); the original 2019 approval also covered FGFR2 fusions, dropped in 2024. The therascreen FGFR RGQ RT-PCR Kit is the companion diagnostic and detects the point mutations R248C, S249C, G370C and Y373C and the FGFR3::TACC3 v1 and v3 fusions from RNA. Sequencing panels report a wider set; the label's word 'susceptible' refers to alterations shown to respond in the trials.

Part ofFGFR3· FGFR3 All readouts

FGFR3: what it is and how drugs act on it · animated schematic, not to scale

Target · the protein and the cell it sits on
Drug · antibody, small molecule, cell or radioligand
Effect · signal, damage or kill

In plain words · A growth-factor receptor that is mutated or fused in a sizeable minority of bladder cancers. Erdafitinib blocks it and is the first targeted drug approved for urothelial cancer selected by a genomic test.

Sequencing 1 approval threshold

What it means for a patient

If your bladder cancer carries one of the FGFR3 changes the label calls susceptible, erdafitinib tablets are on label after one prior treatment (usually chemotherapy or immunotherapy). Eye checks and phosphate monitoring are part of the treatment. Tumours with FGFR3 alterations may respond less well to immunotherapy, which shapes the order of treatments.

Written only from the label or guideline text cited on this page. Not medical advice; your own report and the reading your team gives it come first.

Scoring rule

An FGFR3 point mutation (R248C, S249C, G370C, Y373C) or FGFR3::TACC3 fusion by the therascreen FGFR RGQ RT-PCR Kit, or a susceptible FGFR3 alteration by sequencing.

“Exon 7: R248C (c.742C>T), S249C (c.746C>G); exon 10: G370C (c.1108G>T) and Y373C (c.1118A>G); and fusions ( FGFR3 - TACC3v1 and FGFR3 - TACC3v3 )”
FDA: List of FDA-Authorized Companion Diagnostic Devices

Thresholds used in approvals