Interim analysis of the fierce-21 phase 2 (P2) study of vofatamab (B-701), a selective inhibitor of FGFR3, as salvage therapy in metastatic urothelial carcinoma (mUC).

Abstract

4547 Background: Patients (pts) with mUC with FGFR3 mutations who have failed platinum-based chemotherapy have a poor prognosis. Their response to immune checkpoint inhibitors appears diminished 10% or less compared to WT pts. 20% of mUC pts harbor FGFR3 mutations or fusions (M/F). Vofatamab 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 vofatamab monotherapy (VFM) or in combination with docetaxel (VFD). Methods: The P2 expansion enrolled mUC pts with FGFR3 M/F+ tumor (identified with FoundationONE CDx™), who failed ≥ 1 prior line of chemotherapy (including prior taxane for pts receiving VFM) or recurred ≤ 12 months of (neo)adjuvant chemotherapy. Pts had measurable disease and ECOG ≤ 1. Treatment consisted of vofatamab at 25 mg/kg alone and in combination with docetaxel at 75 mg/m2 q3w. Efficacy was assessed by investigators (RECIST 1.1). Primary objectives were safety and objective response-rate (ORR). Results: In the P2, 21 pts each received VFM and VFD. 57% of VFD pts had received at least 2, and 71% of VFM at least 3 prior lines of therapy. Best response to prior therapy was PD for 67% of VFD and 38% of VFM. The safety profile is consistent with previously reported data. TEAEs occurring in > 20% of pts were decreased appetite, diarrhea, pyrexia, asthenia, anemia, dyspnea, and fatigue. Most common vofatamab-related TEAEs in > 10% of pts were asthenia, diarrhea, decreased appetite and rash; all were Grade 1 or 2. In VFM, only 1 pt had a grade 3 TEAE and no pt discontinued treatment due to an AE. There were no cases of hyperphosphatemia, ocular or nail toxicity; 1 pt reported grade 2 skin toxicity. For pts receiving VM, median age was 70 yrs, ECOG 1 = 67%, Hgb < 10 g/dL 5%, liver metastases 19%. Responses have been seen in 7 pts to date including those receiving both VFM and VFD. Conclusions: Vofatamab both alone and combined with D in a q3w schedule are well tolerated with a low frequency of grade 3 TEAEs. Both VFM and VFD have demonstrated efficacy in terms of ORR. PFS/OS and DOR data will be presented at 7+ months for VFD and 9+ months for VFM. Clinical trial information: NCT02401542.