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).

TPS595 Background: Erdafitinib and enfortumab vedotin are available treatment options in mUC patients with somatic FGFR2/3 GAs after progression on platinum-based chemotherapy and PD-1/L1 inhibitors. However, due to decline in their clinical condition, the sequential delivery of these agents is challenging. Tubulin antagonists induce a G2-M cell-cycle block, while FGFR inhibitors cause a G1 block, with studies suggesting that their combination may be additive or synergistic. Retrospective studies suggest that the activity of EV is not compromised by somatic FGFR2/3 GAs. Hence, there is rationale to evaluate the feasibility of the combination of EV and E, to overcome the difficulties of resistance and sequencing these agents in mUC patients with FGFR2/3 GAs. Methods: This is a phase Ib, single arm, multicenter study in patients with mUC harboring somatic FGFR2/3 GAs who have progressed after platinum and PD-1/L1 inhibitor therapies with enrollment of up to 30 patients. Pts are required to have predominant urothelial component, ECOG-PS 0-2, neuropathy ≤ grade 1 and no ophthalmologic conditions precluding treatment with E. FGFR2/3 GAs may be identified by tumor tissue or circulating tumor (ct)-DNA profiling. The primary objective is feasibility and establishing a recommended phase-2 dose (RP2D). Secondary objectives include objective response rate, duration of response, progression-free survival and overall survival. The dose-escalation component will enroll up to 18 pts with 3+3 design (dosing cohorts in table), followed by dose-expansion component of 12 pts. The dose limiting toxicities (DLTs) will be evaluated using a sequential Bayesian toxicity monitoring that allows a maximum DLT rate of 0.33 during the dose-expansion phase. Exploratory biomarker analyses will be performed including 1) tumor PD-L1, Nectin-4 assessment by immunohistochemistry and association with response 2) ct-DNA evaluation at baseline and progression to evaluate resistance pathways 3) pharmacokinetic studies will assess plasma levels of E and free monomethyl auristatin-E (MMAE). This is led by North American Star Consortium as part of Experimental Therapeutics. Clinical trial information: NCT04963153. [Table: see text]