A Study of Oral Erdafitinib in People With Recurrent Non-Invasive Bladder Cancer

The purpose of this study is to assess the effectiveness of erdafitinib in people with non-muscle invasive bladder cancer (NMIBC) that has come back after standard treatment, such as Bacillus Calmette-Guerin (BCG) or chemotherapy instilled into the bladder. Participants in this study will have bladder cancer with a mutation in the FGFR3 gene. FGFR3 mutations are the most common genetic alteration in NMIBC and is present in the majority of recurrent NMIBC tumors. Genetic testing of the participant's prior or recurrent NMIBC tumor will be performed to confirm it has an FGFR3 gene mutation. Erdafitinib is a pill given orally (by mouth) that blocks the protein made by this altered gene, which may stop cancer cells from growing. Erdafitinib is already used as an approved treatment for metastatic bladder cancer. Researchers are doing this study to determine whether erdafitinib is an effective treatment for FGFR3-altered non-muscle invasive bladder cancer in the time period between when a recurrent tumor is identified and a TURBT (transurethral resection of a bladder tumor) or biopsy procedure is performed to remove it.