Circulating Tumor DNA Clearance Is Associated with Response and Survival in Metastatic Urothelial Carcinoma Treated with First-Line Enfortumab Vedotin Plus Pembrolizumab

Background/Objectives: Enfortumab vedotin plus pembrolizumab (EV+pembro) is the standard first-line treatment for metastatic urothelial carcinoma (mUC), yet no validated on-treatment biomarker identifies patients deriving a durable benefit. We evaluated whether circulating tumor DNA (ctDNA) clearance is associated with response and survival with this regimen alone. Methods: This single-center retrospective study included 25 patients with mUC receiving first-line EV+pembro. A tumor-informed assay (Signatera) measured ctDNA longitudinally. Responses were assessed by RECIST 1.1. Progression-free survival (PFS) and overall survival (OS) hazard ratios (HRs) were estimated by Cox regression and, to address immortal time bias, with clearance as a time-dependent covariate. Results: Fifteen of 25 patients (60%) achieved ctDNA clearance (ever undetectable). The objective response rate was 76% overall and 100% (15/15) with clearance versus 40% (4/10) without (p = 0.0012). Clearance was associated with longer PFS (HR 0.16, 95% CI 0.05–0.54; p = 0.003) and OS (HR 0.08, 95% CI 0.01–0.68; p = 0.021), with similar Firth penalized HRs (0.17 and 0.11). In the time-dependent analysis, the associations were attenuated (PFS HR 0.35, 95% CI 0.09–1.15, p = 0.085; OS HR 0.14, 95% CI 0.01–0.84, p = 0.029; profile likelihood CIs). A post-nadir ctDNA rise preceded progression or death by a median of 95 days in four patients (death in two). Conclusions: In this first-line EV+pembro cohort, all patients who cleared ctDNA responded, and clearance was associated with longer survival, although this association was attenuated in the time-dependent analysis. These hypothesis-generating findings support the prospective evaluation of ctDNA-guided monitoring.