Abstract 3677: Hybrid capture based sequencing from urinary cell free DNA from colorectal cancer patients
Authors: Eberhard Anna , Moser Tina , Ziegler Leandra , Vlachos Georgios , Lazzeri Isaac , Loibner Martina , Gerger Armin , Heitzer Ellen 
Published: March 2024

Abstract
Background: The study of body fluids other than blood is gaining increasing attention in the field of liquid biopsy. Since urine offers a truly non-invasive sampling method, it is a particularly interesting specimen. Evidence suggests that urine cell-free DNA (ucfDNA) harbors information about renal and bladder cancer. However, not much is known about ucfDNA in colorectal cancer (CRC) patients. Therefore, we aimed to test the feasibility of a hybrid capture based NGS approach with and without preanalytical stabilization of urine samples.
Methods: Urine samples were collected from 20 patients with metastatic CRC (mCRC), aliquoted and stored with or without a stabilizing agents (PAXgene Urine Liquid Biopsy Set and Streck urine Preserve) at room temperature. Urine cfDNA was isolated at the day of donation and after 3 days. Matched blood samples were additionally collected in PAXgene Blood ccfDNA Tubes (PreAnalytiX). cfDNA from blood and urine was isolated using the QIAsymphony platform (QIAGEN). cfDNA samples were analyzed using the AVENIO ctDNA Analysis Kit (Roche), a hybrid-capture based approach enriching for 17 clinically relevant genes.
Results: While all stabilized ucfDNA yielded high quality libraries, library preparation failed in 66.7% of unstabilized urine samples, demonstrating that without stabilization ucfDNA rapidly degrades after urine donation. In native samples, in which sequencing data could be obtained, sequencing depth was significantly decreased compared to stabilized samples. For stabilized samples, sequence analysis revealed full concordance between urine and plasma for putative germline variants. However, when using less than 50ng of input material of ucfDNA, a low signal-to-noise ratio with a high number of false positive low level variants was observed. We therefore adjusted the limit of detection for ucfDNA to 0.5%, at which CRC-related mutations were detected in ucfDNA in one patient. Although these variants, were not observed in plasma cfDNA, they could be detected in all stabilized urine samples, which hints to true variants.
Conclusion: Our data demonstrate that a hybrid-capture based analysis approach is feasible for ucfDNA form CRC patients and that urine may provide complementary information about a patient's tumor that may be missed in plasma. Yet, due to degradation and lower concentrations, immediate stabilization of urine after donation is required. Moreover, the limit of detection needs to be adjusted if low amounts of input DNA is available only.
Citation Format: Anna Eberhard, Tina Moser, Leandra Ziegler, Georgios Vlachos, Isaac Lazzeri, Martina Loibner, Armin Gerger, Ellen Heitzer. Hybrid capture based sequencing from urinary cell free DNA from colorectal cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3677.