Objectives We report results of a phase II, open-label study evaluating the combination of pembrolizumab with carboplatin/paclitaxel in previously untreated advanced ovarian cancer patients (NCT02520154).

Methods Eligible patients were women with advanced high-grade epithelial non-mucinous ovarian cancer who had received up to 4 cycles of neoadjuvant carboplatin/paclitaxel chemotherapy and planned for interval cytoreduction. Following interval surgery, patients received adjuvant intravenous carboplatin/weekly paclitaxel/pembrolizumab for 3 cycles then maintenance pembrolizumab until progression, toxicity, or maximum of 20 cycles. The primary endpoint was progression-free survival (PFS). Secondary endpoints included feasibility, toxicity, and overall survival (OS).

Results Twenty-six patients were enrolled with a median follow-up of 26.9 months (range 11.0 – 49.5). Median age was 59 years and predominant histology was high grade serous (88.5%). At interval cytoreductive surgery, complete gross resection (CGR) was achieved in 21 (80.8%); 3 (11.5%) had optimal non-CGR, and 2 (7.7%) had suboptimal cytoreduction. Median PFS was 14.2 months (95% CI 12.4 – 23.0). All patients completed 3 planned cycles of carboplatin/paclitaxel/pembrolizumab. Median number of maintenance cycles was 6 with all 20 cycles completed in 6 patients. Grade 3/4 treatment-related adverse events occurred in 19 (73.1%) patients. Treatment discontinuation due to disease progression occurred in 9 patients (34.6%) and due to immune-related toxicity in 6 patients (28.6%), most commonly attributable to hepatotoxicity (n=3).

Conclusions Combining pembrolizumab with carboplatin/paclitaxel for advanced ovarian cancer patients in the frontline setting was feasible, tolerable, and resulted in PFS within the historical range for this patient population. OS is immature and translational endpoints are pending.