Fierce-21: Phase 1b/2 Study Of Docetaxel + B-701, A Selective Inhibitor Of Fgfr3, In Relapsed Or Refractory (R/R) Metastatic Urothelial Carcinoma (Mucc)

4534Background: Patients with locally advanced or metastatic urothelial carcinoma (mUCC) have a poor prognosis. FGFR3 is frequently overexpressed in UCC and 15-20% of patients with mUCC have FGFR3 gene mutations or fusions (M/F). B-701 is a fully human monoclonal antibody against FGFR3 that blocks activation of the wildtype and genetically activated receptor. FIERCE-21 is a Phase 1b/2 study designed to evaluate B-701 alone or in combination with docetaxel (D). Methods: The study consists of a Phase 1b lead-in (P1b) followed by Phase 2 (P2) expansion and a randomized phase. Eligible patients P1b: the study enrolled mUCC R/R excluding prior taxane treatment, and ECOG u003e 1. Treatment: B-701 at 25 mg/kg and D at 75 mg/m2 q3w. Efficacy was assessed by investigators (RECIST 1.1). Primary objective: Determine P2 dose and evaluate safety and efficacy. Results: 19 patients were enrolled in P1b: median age 66 yrs, ECOG 1 = 58%, Hgb u003c 10 gm/dL 5%, liver metastases 26%, ≥ 2 prior regimens 63%, best response to prior t...