Introduction/Background: Endometrial cancer (EC) is the most common gynecological cancer in the developing world. While significant progress has been made through molecular sub-classification, the treatment of EC for many women remains contentious and better biomarkers are required to guide therapy selection. Circulating tumor DNA (ctDNA) a ‘liquid biopsy’, involves collection of tumor specific DNA via a blood test and can quantify cancer burden and detect tumor specific genomic information. The CODEC study is a prospective pilot study to assess the utility of ctDNA as a prognostic biomarker in EC with the hope that it may help predict relapse and guide selection of adjuvant therapy. Methodology: Women with Type 2 EC planned for surgery and consenting to the collection of biospecimens were enrolled prior to surgery and followed prospectively. Blood was collected perioperatively and then every three months for up to two years and at relapse. Broad sequencing of participants’ tumors was performed, the results of which guided the design of personalized droplet digital PCR (ddPCR) assays for ctDNA analysis. ctDNA was extracted from 5ml of plasma and tested in quadruplicate. PET defined metabolic tumor volume was compared to ctDNA and analysis of ctDNA and relapse free survival (RFS) performed using a Cox proportional hazards regression model. Results: Somatic mutations to guide ddPCR analysis were detected in 45 enrolled women stages 1- 4 including pathogenic variants in POLE. ctDNA results are currently available for 30 participants (remaining results awaited). 12/30 participants had detectable ctDNA preoperatively and 5/25 at Time Point 3 (2-6 weeks post-surgery). ctDNA levels varied significantly across the cohort but results to date indicate that perioperative ctDNA positivity is associated with relapse. Interestingly in those that had detectable ctDNA preoperatively, the majority had a rise in ctDNA intraoperatively. Conclusion: This proof-of-concept analysis showed that ctDNA can successfully be detected in the perioperative setting and is the first study in EC to compare ctDNA with PET findings. Although testing is still underway, the early results indicate that ctDNA maybe a useful biomarker to predict relapse and guide the selection of adjuvant therapy.

Citation Format: Rachel Delahunty, Rainier Arnolda, Thuan Tzen Koh, Michael Hofman, Hayley Johnston, Patricia Wojtowicz, Caitlyn Nguyen, Nicole Brooks, Kym Reid, Julie Lamont, Thomas Jobling, Deborah Neesham, Vanessa Obers, Clair Shadbolt, Brooke Sawyer, Paul Smith, Jennifer Ellis, Geradline Goss, Mila Volcheck, Madawa Jayawardana, Sandun Silva, Chelsee Hewitt, Kate Jones, Andrew Fellowes, Orla McNally, Stephen Wong, Elizabeth Christie, Costas Yannakou. Assessing Circulating TumOur DNA as a prognostic biomarker in endometrial cancer (The CODEC Study) [abstract]. In: Proceedings of the AACR Special Conference on Endometrial Cancer: Transforming Care through Science; 2023 Nov 16-18; Boston, Massachusetts. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(5_Suppl):Abstract nr B019.