A Hispanic man, aged 42 years, was diagnosed with stage IV metastatic urothelial bladder cancer (MUBC) with nonregional lymphadenopathies and lung, bone, and skin involvement. He received first-line treatment with gemcitabine and cisplatin for 6 cycles, achieving a partial response (PR). Next, he received immunotherapy maintenance with avelumab for 4 months until disease progression. A next-generation sequencing test of paraffin-embedded tumor tissue identified a fibroblast growth factor receptor 3 (FGFR3) S249C missense mutation.