Introduction All patients with high grade epithelial ovarian cancer(HGEOC) do not benefit equally from PARP inhibitors, but all are exposed to PARP-associated toxicities. This study aims to assess the correlation between the pathology-based Chemotherapy Response Score(CRS) at the time of interval debulking surgery(IDS) and progression free survival(PFS) in patients who received PARP maintenance, to determine this score’s potential as a marker of expected benefit from PARP.

Methods This is a retrospective cohort study of patients with HGEOC who underwent IDS between January 2016 and September 2022. Demographic and clinical parameters were collected. χ2 test and Student t-test were used to compare descriptive variables and Kaplan-Meier survival analysis with log rank test comparison for PFS.

Results On 169 patients, 47 received PARP maintenance and the majority needed dose reduction due to toxicity(53.2%). Patients with CRS 1(No/Minimal response) or CRS 2–3(Moderate/Complete response) were comparable in terms of baseline characteristics. Patients CRS 1 compared to CRS 2–3 had lower PFS regardless of maintenance(p=0.017). Patients with CRS 2–3 who received PARP showed significantly improved PFS(20 vs 15 months, p=0.029) compared to those who did not, while in those with CRS 1 maintenance was not associated with improved PFS(p=0.27). Results were similar on multivariate analysis, adjusting for BRCA status and surgical outcomes.

Conclusion/Implications In HGEOC patients demonstrating response(CRS 2–3) to NACT, PARP maintenance was associated with a significant improvement in PFS. CRS can be a helpful tool in counseling prior to PARP inhibitor initiation, in patients BRCA-intact, and in settings where homologous recombination deficiency testing is not easily available.