Abstract 5888: Urinary ctDNA tumor fraction monitoring enhances non-invasive assessment of molecular response in bladder-preserving treatment of muscle-invasive bladder cancer

Introduction: While radical cystectomy (RC) following neoadjuvant therapy remains the standard of care for muscle-invasive bladder cancer (MIBC), bladder-preserving treatments offer a viable option for selected patients to improve quality of life. Rapid detection of therapeutic response is critical for clinical decision-making but remains challenging. Here, we introduce a non-invasive liquid biopsy assay based on next-generation sequencing (NGS) to monitor the molecular response in both urine and blood during neoadjuvant therapy in MIBC patients. Methods: This ongoing trial has enrolled 20 patients treated with HER2 ADC neoadjuvant therapy, followed by radiotherapy and clinical evaluation to decide between RC or bladder preservation. In a completed pilot cohort of seven patients, both urine and blood samples were collected before and after HER2 ADC treatment to evaluate therapy response. The study utilized PredicineCARE, a targeted NGS assay, to analyze circulating tumor DNA (ctDNA) in urine and blood samples, aiming to detect genetic variations and evaluate tumor fractions in patients. Results: In the pilot cohort of seven patients, the ctDNA assay detected a greater number of somatic mutations and exhibited higher detection positivity in urine samples compared to blood samples. Specifically, in urine samples, the assay identified 138 somatic mutations at baseline and 18 mutations at the end of therapy, achieving positivity in all seven patients at both time points. In contrast, in blood samples, it identified 11 mutations at baseline and 6 mutations at the end of therapy, with positivity in 5 out of 7 and 4 out of 7 patients, respectively. The overall tumor fractions detected in urine samples were significantly higher at baseline than at the end of therapy (median tumor fraction: baseline 10.6% vs. end of therapy 0.8%; p=0.043), a trend not observed in blood samples. Moreover, through paired comparisons of each patient's urine samples at the two time points, we observed a molecular response—defined as a tumor fraction decrease greater than 20%—in six of the seven patients, and molecular progression—defined as a tumor fraction increase greater than 20%—in one patient. These findings were consistent with the clinical evaluations conducted at baseline and at the end of therapy. Conclusion: Our study demonstrates that urine-based ctDNA analysis using a non-invasive liquid biopsy assay provides a reliable method for monitoring molecular response during neoadjuvant therapy in patients with MIBC undergoing bladder-preserving treatments. These findings suggest that urine ctDNA analysis can serve as a valuable tool for rapid detection of therapeutic response, aiding clinical decision-making. Further validation in larger cohorts is warranted to establish its utility in routine clinical practice. Citation Format: Jiani Deng, Feng Wen, Haoran Tang, Cancan Jia, Yue Zhang, Peng Zhang, Yali Shen. Urinary ctDNA tumor fraction monitoring enhances non-invasive assessment of molecular response in bladder-preserving treatment of muscle-invasive bladder cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5888.