Phase Ib trial of erdafitinib (E) combined with enfortumab vedotin (EV) following platinum and PD-1/L1 inhibitors for metastatic urothelial carcinoma (mUC) with FGFR2/3 genetic alterations (GAs).

Abstract

625 Background: Erdafitinib (E) is a treatment option in mUCpatients with somatic FGFR2/3 GAs after progression on platinum-based chemotherapy (PBC). Enfortumab Vedotin (EV) is approved as a single agent to treat mUC patients following prior PBC and PD1/L1 inhibitors or as second-line therapy for cisplatin-ineligible patients. Retrospective studies suggest that the activity of EV is not compromised by FGFR2/3 GAs. E and EV have different mechanisms of activity, and toxicities are mostly non-overlapping. Hence, there is rationale to evaluate the feasibility of combination E + EV, to overcome the difficulties of resistance and sequencing agents in mUC patients with FGFR2/3 GAs. Methods: This is an ongoing, single arm, multicenter, dose-escalation and expansion study of combination E + EV evaluating the safety, tolerability, pharmacokinetics (PK), and antitumor activity in patients with mUC harboring somatic FGFR2/3 GAs who have progressed after PBC and/or PD1/L1 inhibitor therapies. Dose escalation phase aims to identify the maximum tolerable dose and recommended phase 2 dose of EV at dose levels of 1 mg/kg and 1.25 mg/kg in combination with E at 8 mg/day as shown in the table. Preliminary safety, PK, and efficacy data for Dose Level (DL) 1 and 2 are presented in this abstract. Results: As of data cutoff, based on 3+3 design, total 8 patients are enrolled and finished dose limiting toxicity (DLT) period (1st cycle). Six patients were enrolled in DL1 with 1 DLT (skin rash) and 2 patients in DL2. The most common treatment-related adverse events (TRAE) included hyperphosphatemia (88%), mucositis (88%), hypercalcemia (75%), high AST (75%), hand foot syndrome (75%), peripheral neuropathy (75%), alopecia (63%), diarrhea (63%), hypoalbuminemia (63%) and hypomagnesemia (63%). Grade 3 TRAE included hand foot syndrome (50%), anemia (17%), rash (17%), anorexia (17%) and paronychia (17%). One patient developed grade 4 Stevens-Johnson syndrome related to EV which subsequently improved. PK data are available for all 6 subjects in DL1. The average steady-state Cmin of E and monomethyl auristatin E (MMAE) was 1430 ± 639 ng/mL and 1.4 ± 0.9 ng/mL, respectively, and the average Cmax of MMAE was 3.9 ± 0.9 ng/mL at DL1. All 8 patients are evaluable for response, and best response is partial response in all. Detailed safety and additional efficacy data will be presented. Conclusions: Combination E + EV is feasible and preliminarily exhibits antitumor activity. Dose escalation is ongoing to identify the MTD or recommended dose for expansion of the trial. Clinical trial information: NCT04963153 . [Table: see text]