Inclusion Criteria:  Subjects with a diagnosis of locally advanced or metastatic bladder caner Documented proof of an FGFR alteration according to a CLIA-based test Subjects who are receiving or will receive erdafitinib as their standard medical therapy as a monotherapy or in combination Age greater than or equal to 18 years. Subject is a resident of or seeking care in the United States Able and willing to provide informed consent to this biomarker study Informed consent obtained for the XCELSIOR longitudinal outcomes registry (NCT03793088).  Exclusion Criteria:  Subjects younger than 18 years of age Subjects unwilling or unable to provide informed consent Subjects that are not receiving treatment in the United States or US Territories