Introduction Standard treatment for epithelial ovarian cancer involves surgery and platinum-based chemotherapy, but recurrence or disease progression still occurs in over 70% of patients. CtDNA-based MRD testing may be a potential biomarker for disease surveillance.

Methods Primary ovarian cancer with stage II-IV of HGOC patients was recruited in this study. Tumor sample was collected for whole exome sequencing (300x). Proprietary algorithm was used to select 30–40 single nucleotide variants for each patient. Blood was collected and MRD was detected by multiplex PCR-based sequencing (OriMIRACLE S^TM, 100,000x) using the customized panel (NCT05027828).

Results As of the summary submission, we have completed WES sequencing for 20 patients, of which 11 carry HRR pathway mutations. Among the 13 patients who underwent pre- and post-operative ctDNA monitoring, 11 were ctDNA positive before surgery. We found a significant decrease in ctDNA variant allele frequency (VAF) before and after surgery (before: median VAF 0.95%, after: median VAF 0.04%, p=0.0054). Additionally, Pearson correlation analysis showed a positive correlation between pre-treatment ctDNA VAF and CA125 levels (R=0.685, p=0.017). The median VAF of ctDNA in stage IV patients was higher than that in stage I-III patients (2.14% vs. 0.56%, p=0.69). All the 13 patients were negative for MRD after completion of chemotherapy. Follow-up is ongoing.

Conclusion/Implications MRD testing is feasible for monitoring epithelial ovarian cancer patients, with over 80% of HGSOC patients being MRD-positive at baseline. The MRD status was generally consistent with the clinical status of the patients. The performance of MRD in predicting recurrence of HGSOC is still under investigation.