(UroToday.com) FGFR3 has been one of the most heavily studied and scrutinized proteins along the continuum of urothelial carcinogenesis. Mutations in receptor tyrosine kinases have been described in up to 30% of muscle-invasive bladder cancer (MIBC), with FGFR3 being implicated in more than 50% of these cases. Rates of FGFR3 mutations vary considerably by stage and grade, with mutations in non-muscle-invasive bladder cancer (NMIBC) ranging from 60-70%.1