Holash, Jocelyn

4540 Background: Patients w/ locally advanced or metastatic urothelial carcinoma (UCC) have a poor prognosis. Prior to atezolizumab’s approval, there were no approved treatments (txs) for pts who progressed after chemotherapy. Even w/ immune checkpoint inhibitors, most pts require additional txs. FGFR3 is frequently overexpressed in UCC and 15-20% of pts w/ advanced disease have tumors w/ FGFR3 gene mutations or fusions. B-701 (formerly R3Mab) is a fully human monoclonal antibody against FGFR3 that blocks activation of the wildtype and genetically activated receptor. NCT02401542 is a phase (ph) 1b/2 study designed to evaluate the safety and efficacy of B-701 plus docetaxel (D) in advanced UCC pts. Methods: The study has a lead-in (n=20 pts) and a randomized ph (n=201). Eligible pts: Stage IV UCC, relapsed/refractory to 1 or 2 prior chemotherapy regimens not including taxanes with ECOG 0-1. Txs: B-701 at 25 mg/kg q3w (+ loading dose on C1D8) and D at 75 mg/m2 q3w. Efficacy assessed by RECIST 1.1. Primary obj: PFS and safety. Secondary obj: overall response rate (ORR); duration of response (DOR); disease control rate (DCR); overall survival (OS). Exploratory obj: association of FGFR3 status w/ efficacy and AEs. Results: As of 20 Jan 2017, 19 pts enrolled to lead-in ph w/median age 66 yrs, ECOG 1 58%, Hgb <10 gm/dL 5%, liver mets 26% and ≥ 2 prior regimens 63%. 17 evaluable for PFS/ORR. 5 pts w/ FGFR3 mut or TACC3-fus. Gr ≥3 AEs occurring in ≥2 pts: decreased neutrophils (26.3%), neutropenia (10.5%), decreased WBCs (10.5%). 2 pts had D dose reductions and 1 pt discontinued tx due to AE (disseminated intravascular coagulation). Conclusions: Preliminary results show that B-701 combines safely and effectively with D in UCC, with the combination being well tolerated and showing promising ORR and PFS in pts w/ FGFR3 mut/fus. The protocol has been amended to add Cohorts 2 (B-701+D) and 3 (B-701) (n=20 pts/cohort) for pts w/ FGFR3 mut/fus+ tumors only. Clinical trial information: NCT02401542. [Table: see text]