Objectives The aim of the study was to investigate the correlation of chemotherapy response score (CRS) after neoadjuvant chemotherapy (NACT) to treatment outcomes in ovarian cancer (OC).

Methods Chemotherapy response score was retrospectively determined on pathology slides of all patients with epithelial OC that had interval debulking surgery (IDS) between 2009–2014. Chemotherapy response score 1 was given when tumor was present and infiltrated by inflammatory cells, CRS 2 when both tumor and regressive chemotherapy changes were present, and CRS 3 when scant tumor was seen within extensive chemotherapy-induced changes. Patients’ characteristics including survival data were collected and compared between CRS groups.

Results Pathology slides of 132 patients were reviewed. Forty-nine patients had CRS 1, 65 had CRS 2, and 18 had CRS 3. Age, stage, and grade were not different across CRS groups. A higher percent of CRS 1 and 2 patients required more than 3 cycles of NACT, whereas CRS 3 patients had higher rates of no residual disease at completion of IDS. Chemotherapy response score 3 group showed the most significant CA125 decrease after NACT (97% decrease, P = 0.016). Kaplan-Meir survival curves showed a significantly longer progression-free survival but not overall survival for patients with CRS 3 (median progression-free survival = 7.5, 12, and 17 months for CRS 1, 2, and 3, respectively, P = 0.012), and this remained statistically significant in both univariate and multivariate analysis. Interobserver reproducibility for CRS was good (weighed κ = 0.762).

Conclusions Patients with CRS 3 have longest progression-free survival and highest CA125 drop after NACT. These parameters have important prognostic value and can be used for clinical decision-making.