FGFR3 has been found to be mutated in up to 64% of cases of bladder cancer; 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. FGFR3 mutations (including Y373C) 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. Targeted therapies with FGFR3 inhibitors have been explored in patients with bladder cancer.