Longitudinal Monitoring of Circulating Tumor DNA to Assess the Efficacy of Immune Checkpoint Inhibitors in Patients With Advanced Genitourinary Malignancies

PURPOSE: Circulating tumor DNA (ctDNA) detection in blood has emerged as a prognostic and predictive biomarker demonstrating improved assessment of treatment response in patients receiving immune checkpoint inhibitors (ICIs). Here, we performed a pilot study to support the role of ctDNA for longitudinal treatment response monitoring in patients with advanced genitourinary (GU) malignancies receiving ICIs. MATERIALS AND METHODS: Patients with histologically confirmed advanced GU malignancies were prospectively enrolled. All eligible patients received ICI treatment for at least 12 weeks, followed by serial collection of blood samples every 6-8 weeks and conventional scans approximately every 12 weeks until disease progression. ctDNA analysis was performed using Signatera, a tumor-informed multiplex-polymerase chain reaction next-generation sequencing assay. Overall, the objective response rate (ORR) was reported and its association with ctDNA status was evaluated. Concordance rate between ctDNA dynamics and conventional imaging was also assessed. RESULTS: ctDNA analysis was performed on 98 banked plasma samples from 20 patients (15 renal, four urothelial, and one prostate). The median follow-up from the time of initiation of ICI to progressive disease (PD) or data cutoff was 67.7 weeks (range, 19.6-169.6). The ORR was 70% (14/20). Eight patients ultimately developed PD. The overall concordance between ctDNA dynamics and radiographic response was observed in 83% (15/18) of patients. Among the three patients with discordant results, two developed CNS metastases and one progressed with extracranial systemic disease while ctDNA remained undetectable. CONCLUSION: In this pilot study, longitudinal ctDNA analysis for monitoring response to ICI in patients with advanced GU tumors was feasible. Larger prospective studies are warranted to validate the utility of ctDNA as an ICI response monitoring tool in patients with advanced GU malignancies.