866 Background: Circulating tumor DNA (ctDNA) is an emerging biomarker for monitoring treatment response and minimal residual disease (MRD) in urothelial carcinoma (UC). Serial ctDNA assessment enables real-time tracking of molecular response to therapy. Enfortumab vedotin plus pembrolizumab (EVP) demonstrates strong activity across advanced and localized UC. Ultrasensitive, tumor-informed, whole-genome ctDNA assays offer a highly sensitive approach to quantify molecular response and assess ctDNA clearance as a potential biomarker of exceptional therapeutic benefit and a tool for treatment de-escalation. Methods: Single-institution, retrospective analysis of patients (pts) with UC, including metastatic, inoperable, or localized cisplatin-ineligible muscle-invasive bladder cancer (MIBC) or upper tract urothelial carcinoma (UTUC), treated with EVP. Plasma ctDNA was analyzed using the Next Personal Dx tumor-informed whole-genome sequencing assay, tracking up to 1,800 patient-specific variants with detection down to ~1 part per million. Clinical response was assessed by imaging and cystoscopy, and longitudinal ctDNA levels were correlated with outcomes. ctDNA clearance was defined as undetectable ctDNA at any post-treatment timepoint. Results: Twenty-seven patients with 118 plasma samples were analyzed. Median age was 71 years (range 34–89); 78% were male and 7% Black. Disease site included 22 (81%) MIBC and 5 (19%) UTUC; 17 (63%) had metastatic disease, 9 (33%) received neoadjuvant EVP, and 1 (4%) received adjuvant therapy. Median number of EV cycles was 6 (range 2–12). At the time of analysis, 11 complete responses (42%), 11 partial responses (42%), 3 stable disease (12%), and 1 progressive disease (4%). Pre-EVP ctDNA was available for 18 (67%); 4 (22%) were ctDNA-negative pre-EVP. Among evaluable patients, 11 (48%) achieved ctDNA clearance after a median of 3 EVP cycles (range 1–11), while 12 (52%) had persistent ctDNA positivity. Median follow-up was 13.8 months (range 5.5–48.3); 19 (70%) remain under surveillance, including 9 with metastatic disease. Conclusions: Tumor-informed whole-genome ctDNA kinetics represents a feasible and highly sensitive biomarker of response to EVP in UC. ctDNA clearance correlated with exceptional clinical and radiographic outcomes, whereas persistent ctDNA positivity identified residual or progressive disease. These findings support the use of ultrasensitive ctDNA dynamics for real-time treatment monitoring and as a potential tool for response-based de-escalation strategies. Prospective studies are warranted to validate ctDNA clearance as a biomarker of durable response in UC.
Zerey et al. (Sun,) studied this question.