Introduction Epithelial ovarian cancer (EOC) is a lethal gynecologic cancer, with high recurrence rate despite the use of target therapy such as poly ADP-ribose polymerase inhibitor (PARPi). Circulating tumor DNA (ctDNA) is a promising biomarker for detecting minimal residual disease (MRD) in solid tumors. We aimed to investigate the use of ctDNA to detect MRD in patients with EOC who underwent long-term PARPi maintenance treatment.

Methods We prospectively identified 21 patients with EOC who had received PARPi maintenance for over two years. Tissue testing for individual mutation marker was performed with TruSight Oncology panel from Illumina and follow-up ctDNA testing was performed with Pan100 panel from Dxome or small custom panel with high-depth sequencing.

Results A total of 21 patients received different types of PARPi (olaparib, n=12; niraparib, n=7; rucaparib, n=1; and talazoparib, n=1) for a median of 27 months. Twelve patients had germline BRCA mutation, two had somatic BRCA mutation, and one had loss of heterozygosity. MRD was only detected in one patient, who experienced recurrence 3 months after ctDNA evaluation. Among them, two patients experienced recurrence. The other patient had recurrence 7 weeks after ctDNA evaluation without evidence of MRD, suggesting a negative predictive value of 0.905, and a positive predictive value of 1.00.

Conclusion/Implications Our findings suggest that ctDNA can be used to monitor MRD in EOC patients undergoing long-term PARPi maintenance treatment, allowing clinicians to tailor the duration of PARP inhibitor based on patient-specific molecular findings. Further data with additional patients and survival maturation will be presented at the conference.