Balversa (erdafitinib) has been FDA approved for treatment of urothelial carcinoma with susceptible FGFR3 or FGFR2 genetic alterations. FGFR3 is a receptor tyrosine kinase in the RAS-MAPK and PI3K-AKT pathways. FGFR3 has been found to be mutated in up to 64% of cases of bladder cancer and 40% of upper urothelial tract (ureter and renal pelvis) urothelial carcinomas. FGFR3 mutations tend to be exclusive of RAS mutations ,TP53 overexpression, TP53 mutation, but not PIK3CA mutations. However, subsets of cases with co-mutations have been described. Gain of function FGFR3 mutations (including FGFR3 R248C and FGFR3 S249C) are believed to lead to constitutive activation of the receptor and activation of the RAS-MAPK pathway. FGFR3 mutations are often seen in non-muscle invasive bladder cancers and tend to correlate with low stage and grade; however, FGFR3 mutations have also been described in muscle-invasive bladder cancer.