Abstract 3368: Homologous Recombination Deficiency (HRD) Testing on Cell-Free Tumor DNA in Ascites of Patients with Newly Diagnosed Advanced Epithelial Ovarian Cancer

Abstract Background: Knowledge regarding the homologous recombination deficiency (HRD) status at diagnosis is essential to manage patients (pts) with advanced epithelial ovarian cancer (EOC). HRD is defined by either a BRCA1 or BRCA2 mutation, or genomic instability (GI). These genomic tests are performed on FFPE tumor samples and unfortunately non-contributive in 12-18% of cases. Advanced OC frequently presents with ascites which could provide an alternative source of Cell-free tumor DNA (cftDNA). Methods: We collected data from 53 patients undergoing primary (N=35) or interval (N=12) laparoscopy for suspected/confirmed EOC, or abdominal paracentesis at relapse (N=6). cftDNA was extracted from 20ml of ascites, or 20ml of peritoneal washings if no ascites was present. Intraperitoneal cfDNA was subjected to next generation sequencing (NGS) to confirm tumoral origin and to identify BRCA1/2 mutations, and GI was assessed by measuring large scale genomic alterations on shallow Whole Genome Sequencing (sWGS). Matching FFPE tumor samples underwent NGS and GI testing. Results: A total of 53 patient were included. Overall, intraperitoneal cfDNA was detectable in more than 90% (48/53) pts, and in 100% (35/35) of pts at diagnosis. Even among patients without visible ascites, peritoneal washings yielded cfDNA in 40% of cases (3/7). DNA quality (presence of mononucleosomal pics around 160bp and low contamination with high molecular DNA greater than 700bp) and quantity (median concentration: 3700 ng/ml; range 109 - 65 000 ng/ml) was excellent and median turn-around testing time was 21 days. Ascitic cfDNA was confirmed as tumoral in 98% of cases, largely due to detection of TP53 mutations (85,5%, 41/48), other variants in cftDNA included. Seven (15%) and 6 (12,5%) patients had BRCA1 and BRCA2 mutations, respectively. For 36 pts, NGS results on matching tumor tissue were available, and among those 97% (35/36) had concordant mutations detected in ascitic cftDNA and tumor tissue DNA. In 5 pts for whom tumor tissue-based NGS was non-contributive, NGS on cftDNA from ascites was informative and uncovered a BRCA2 mutation in one pt. We then performed GI testing on 18 cftDNA samples using sWGS and 100% of samples yielded contributive GI test results. Of these 18 pts, 42% (7/18) has failed GI testing on matching tumor sample. Conclusion: Genomic profiling on cftDNA from ascites is feasible, yields high quality and quantity tumor derived cfDNA. Importantly this approach has a fast testing turn-around time and only requires 20ml of ascites so that the majority of pts with advanced OC would be eligible to this approach. This cftDNA is suitable for HRD testing combining both BRCA mutation analysis and GI testing and should be done in every patient at primary laparoscopy Citation Format: Cyril Roussel-Simonin, Felix Blanc-Durand, Etienne Roueau, Audrey Le Formal, Laure Chardin, Elisa Yaniz, Sebastien Gouy, Amandine Maulard, Stéphanie Cherrier, Claire Sanson, Lea Mauny, Sophie Coterret, Francois Zaccarini, Roseline Tang, Alexandra Leary. Homologous recombination deficiency (HRD) testing on cell-free tumor DNA in ascites of patients with newly diagnosed advanced epithelial ovarian cancer [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 3368.