An academic multimodal ctDNA strategy for minimal residual disease detection and therapy monitoring in advanced epithelial ovarian cancer: Insights from the phase IV IOLANTHE trial.

e17547 Background: Sensitive detection of minimal residual disease (MRD) and longitudinal monitoring of treatment response remain critical unmet needs in advanced epithelial ovarian cancer (EOC). ALMA (Agnostic Liquid Biopsy Multi-modal Advancement) is a tumor-agnostic circulating cell-free DNA (cfDNA) platform that integrates multiple orthogonal features—tumor fraction (TF), fragmentomic profile, methylation patterns, and somatic copy number alterations (SCNAs)—to improve MRD detection and disease monitoring. Here, we assessed the clinical feasibility of ALMA in patients with advanced EOC who underwent cytoreductive surgery and were treated with platinum-based chemotherapy plus bevacizumab, with or without olaparib as maintenance therapy within the phase IV IOLANTHE trial (NCT06121401). Methods: Plasma samples were prospectively collected at predefined longitudinal time points. Baseline samples were obtained from all patients prior to any surgical intervention or chemotherapy. A second time point was collected following surgery, either primary debulking (PD) or interval debulking (ID). Additional samples were collected at the end of chemotherapy and at 12 weeks after initiation of maintenance therapy. Whole-genome cfDNA sequencing was performed using a dual strategy: low-pass WGS for TF estimation, fragmentomic profiling, and SCNA detection, and bisulfite-free methylation sequencing (cf-MBD-seq) for genome-wide methylation analysis. To date, the enrollment of IOLANTHE trial has been completed, and 192 patients were included. Results: A total of 55 longitudinal plasma samples were analyzed from 32 patients. Following size-based ctDNA enrichment, TF detection was achieved in 100% of analyzed samples. Mean TF decreased longitudinally from 17.28% at baseline (n=25), to 6.31% after PD or ID surgery (n=19), 5.08% at completion of chemotherapy (n=8), and 3.80% at 12 weeks of maintenance therapy (n=3). Genome-wide methylation profiling identified 2857 differentially methylated regions (adjusted p<0.01), of which 68% were located within CpG islands, predominantly in promoter regions. Conclusions: The ALMA approach proved to be feasible. Analyses of further cases are in progress and the results are expected to be presented at the meeting. Clinical trial information: NCT06121401 .