This is a Phase 1b/2, randomized, double-blind, placebo-controlled, multicenter, parallel-group, efficacy and safety study of B-701 plus docetaxel versus placebo plus docetaxel in the treatment of subjects with Stage IV, locally advanced or metastatic UCC who have relapsed after, or are refractory to at least one prior line of chemotherapy. This study is divided into 2 phases: Lead-In Phase and Randomized Phase; and the Lead-In Phase is divided into 3 cohorts. In Cohorts 1 and 2, all subjects will receive both B-701 plus docetaxel (unblinded). In Cohort 3, all subjects will receive B-701 only (unblinded). Subjects enrolling in Cohorts 2 and 3, as well as the Randomized Phase of the study, must have tumors with FGFR3 mutations or gene fusions.