Aim The purpose of this study was to investigate whether the Ki67 values were associated with survival for predicting prognosis in patients with advanced ovarian cancer receiving neoadjuvant chemotherapy (NACT). Methods Among 17 patients treated with NACT, 13 patients were available for tissue samples from matched pre‐ and post‐therapy tissues. Ki67 scores were transformed to a logarithmic scale for the statistical analyses. The optimal cutoff values of the log‐phase Ki67 were assessed by receiver operating characteristic (ROC) analysis. Kaplan–Meier analysis, the log‐rank test, and Cox regression analysis were carried out to analyze survival. Results The Ki67‐decrease and post‐NACT Ki67 were the independent factors associated with relapse‐free survival (RFS) (p < 0.001 and p = 0.003). No association was observed on overall survival. The optimal cutoff values for the Ki67‐decrease and the post‐NACT Ki67 were 6.67% and 5.46 based on ROC where the area under ROC curves (AUC) were 1.00 (p < 0.001) with the 100% sensitivity and specificity. The median RFS was 537 days in patients showing Ki67‐decrease >6.66% or post‐NACT Ki67 level <5.46, while it was 224 days in those with Ki67 decrease ≤6.66% or post‐NACT Ki67 level ≥5.46 (p = 0.001). Conclusions The Ki67‐decrease and the lower post‐NACT Ki67 are independent factors associated with favorable RFS, indicating that they could be precise biomarker candidates for prognosis in NACT‐administered patients with advanced ovarian cancer.

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