Abstract 2306: Potential clinical utility of circulating tumor DNA detected by digital PCR in a nationwide Danish cohort of high-risk colorectal cancer patients

Abstract Introduction: Increasingly, circulating tumor DNA (ctDNA) is proposed as a tool for minimal residual disease (MRD) assessment, with the potential to guide postoperative treatment decisions. Low ctDNA levels immediately after surgery necessitate extremely sensitive detection methods. Additionally, for potential clinical implementation, detection methods should ideally feature short turnaround times (TATs) and low analysis costs. Compared to sequencing-based detection methods, digital PCR is low-cost, and features TATs of less than a day. Consequently, digital PCR is a good candidate for clinical implementation. Here, we present ctDNA detection results from a highly optimized, tumor-informed digital PCR strategy in a large cohort of stage II-III colorectal cancer (CRC) patients. Methods: Stage II-III CRC patients (n=864) treated with curative intent were recruited from Danish surgical centers from 2014 to 2021. Whole exome sequencing was conducted on matched tumor and buffy coat from all patients. After thorough clonality assessment, a mutational target was chosen for digital PCR analysis. Plasma samples (8mL) collected before and within 60 days after surgery, were investigated for ctDNA using digital PCR. Additionally, a subset of patients (n=229) had serial samples collected every three months analyzed for ctDNA. Results: Before surgery, ctDNA was detected in 569/828 (69%) analyzed blood samples. A minimum of 12 months of radiological follow-up was available for 598/864 patients at time of writing, enabling prognostic evaluation of ctDNA detection in these patients. Postoperative ctDNA detection was highly correlated to future recurrence (HR=9.6, 95%CI 6.3-15, P<0.001). The median time to recurrence was significantly shorter for postoperatively ctDNA positive patients (10 months, interquartile range (IQR) 3.8-12 months) compared to ctDNA negative patients (18 months, IQR 12-26 months, P<0.001), indicating a higher disease burden postoperatively in ctDNA positive patients. In a subset of patients with samples collected immediately after adjuvant treatment (n=95) and serially (n=186), ctDNA was also prognostic of recurrence (HR=6.4, CI95% 2.9-14, P<0.001; HR=27, 95%CI 14-52, P<0.001). A minimum of 12 months of follow-up is expected to be available for 700 patients before the AACR meeting 2023. Conclusion: These results from one of the largest ctDNA detection cohorts of stage II-III CRC patients demonstrate that our personalized digital PCR approach effectively detects MRD immediately after surgery. Additionally, our approach shows promise for serial ctDNA detection for recurrence surveillance applications. With digital PCR being a widespread and cost-effective method with low TATs, clinical implementation of ctDNA analysis may be more forthright using this method over cost-intensive sequencing-based methods. Citation Format: Tenna V. Henriksen, Christina Demuth, Amanda Frydendahl, Marijana Nesic, Mads H. Rasmussen, Thomas Reinert, Ole H. Larsen, Anders H. Madsen, Uffe S. Løve, Per V. Andersen, Ole Thorlacius-Ussing, Ismail Gögenur, Jakob Lykke, Allan G. Pedersen, Peter Bondeven, Nis H. Schlesinger, Lene H. Iversen, Kåre A. Gotschalck, Claus L. Andersen. Potential clinical utility of circulating tumor DNA detected by digital PCR in a nationwide Danish cohort of high-risk colorectal cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2306.