Abstract 3398: Exploring the biology of ctDNA release in colon cancer

Background: Colorectal cancer is responsible for 9.4% of cancer-related deaths worldwide. Early detection of the disease has the potential to improve patient outcomes, therefore, developing an efficient and minimally invasive method for carrying out surveillance has been a clinically relevant effort in recent years. Circulating tumour DNA has garnered interest as a marker for early cancer detection, however, deeper understanding of the underlying biology of ctDNA release is needed in order to maximize its utility in clinical practice. In this project, we aimed to investigate whether a phenotype conductive to ctDNA shedding can be defined in a colorectal cancer cohort, including transcriptomic, genomic and clinical data collected from stage I to stage IV colon cancer patients at Aarhus University Hospital. Methods: Transcriptomic data from 102 patients and whole exome sequencing data from 60 patients were analyzed. Differential gene expression and differential pathway enrichment analyses between ctDNA positive and ctDNA negative patients were conducted by performing Student’s t-test. The resulting p-values were adjusted according to the Benjamini-Hochberg method. The genes in the transcriptomic analyses were assigned to pathways with regard to the MSigDB Hallmark gene sets and pathway enrichment was assessed using Gene Set Variation Analysis (GSVA). Using an extended cohort of 537 patients, we performed Wilcoxon’s signed rank test to investigate the association between tumour size, histological subtypes and ctDNA shedding behavior. Additionally, we modelled the expected ctDNA fraction as a function of birth rate, death rate and tumour mass. Results: In colon cancer, ctDNA release is primarily associated with tumour size, molecular subtypes and proliferative transcriptomic signatures. A moderate but significant correlation was observed between the tumour’s largest diameter and the detected ctDNA fraction. Furthermore, molecular subtypes associated with less aggressive disease tended to shed lower amounts of ctDNA. Notably, we have found that pathways associated with proliferation are enriched in the ctDNA positive subgroup. Conclusions: Our results demonstrate that enhanced proliferative capacity in connection with tumour size and molecular subtypes may contribute to a higher ctDNA release rate. We anticipate our study to be a starting point for further investigation of ctDNA shedding dynamics in colorectal cancer. Citation Format: Judit Kisistok, Tenna Vesterman Henriksen, Jesper Bertram Bramsen, Thomas Reinert, Trine Block Mattesen, Nicolai Juul Birkbak, Claus Lindbjerg Andersen. Exploring the biology of ctDNA release in colon cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3398.