Higher expression of CDK9 was present in metastatic and recurrent ovarian cancer tissues compared with patient-matched primary tumors and correlated with poor patient prognosis. A) Distribution of CDK9 immunohistochemical staining scores among primary, metastatic, and recurrent ovarian cancer tissues. B) Expression of CDK9 between primary and paired metastatic tissues. Red signifies increased, black signifies equal, and green signifies decreased. C) Expression of CDK9 between primary and paired recurrent tissues. D, E) Correlation between expression of CDK9 in the primary ovarian cancer tissues (Weak: CDK9 staining ≤2+; Strong: CDK9 staining ≥3+) and DFS (D) or OS (E) in ovarian cancer patients by Kaplan-Meier survival curve analysis. F) Representative images of hematoxylin and eosin (HE) and nuclear staining intensity for CDK9 in matched primary, metastatic, and recurrent ovarian cancer tissues. CI, confidence interval; HR, hazard ratio.