RB1 and urothelial carcinoma: Prior studies found FGFR3 mutations to be present in approximately 70% to 80% of low-grade, low-stage papillary urothelial carcinomas, and they often occur in combination with PIK3CA mutations.19,21,22 Additionally, CDKN2A homozygous deletion has been shown to be linked to progression in FGFR3-mutated urothelial carcinoma.23,24 On the other hand, TP53 and RB mutations are known to be driving oncogenesis in high-grade, high-stage urothelial carcinomas.