Antitumor activity and safety of pembrolizumab in patients with advanced recurrent ovarian cancer: results from the phase II KEYNOTE-100 study

BACKGROUND: Advanced recurrent ovarian cancer (ROC) is the leading cause of gynecologic cancer-related death in developed countries and new treatments are needed. Previous studies of immune checkpoint blockade showed low objective response rates (ORR) in ROC with no identified predictive biomarker. PATIENTS AND METHODS: This phase II study of pembrolizumab (NCT02674061) examined two patient cohorts with ROC: cohort A received one to three prior lines of treatment with a platinum-free interval (PFI) or treatment-free interval (TFI) between 3 and 12 months and cohort B received four to six prior lines with a PFI/TFI of ≥3 months. Pembrolizumab 200 mg was administered intravenously every 3 weeks until cancer progression, toxicity, or completion of 2 years. Primary end points were ORR by Response Evaluation Criteria in Solid Tumors version 1.1 per blinded independent central review by cohort and by PD-L1 expression measured as combined positive score (CPS). Secondary end points included duration of response (DOR), disease control rate (DCR), progression-free survival (PFS), overall survival (OS), and safety. RESULTS: Cohort A enrolled 285 patients; the first 100 served as the training set for PD-L1 biomarker analysis. Cohort B enrolled 91 patients. ORR was 7.4% for cohort A and 9.9% for cohort B. Median DOR was 8.2 months for cohort A and not reached for cohort B. DCR was 37.2% and 37.4%, respectively, in cohorts A and B. Based on the training set analysis, CPS 1 and 10 were selected for evaluation in the confirmation set. In the confirmation set, ORR was 4.1% for CPS