Pembrolizumab monotherapy in Japanese patients with advanced ovarian cancer: Subgroup analysis from the KEYNOTE‐100

Interim results from the two‐cohort, phase 2 KEYNOTE‐100 study (NCT02674061) of 376 patients with previously treated advanced recurrent ovarian cancer (ROC) showed that pembrolizumab monotherapy was associated with an objective response rate (ORR) of 8.0% (95% CI, 5.4‐11.2). We present outcomes for the Japanese patients (n = 21) enrolled in KEYNOTE‐100. Patients with epithelial ROC had received either 1‐3 prior chemotherapy lines and had platinum‐free interval or treatment‐free interval (PFI; TFI) of 3‐12 months (cohort A) or 4‐6 prior chemotherapy lines and had PFI/TFI of ≥3 months (cohort B). All patients received pembrolizumab 200 mg every 3 weeks as monotherapy for 2 years or until progression, death, unacceptable toxicity or consent withdrawal. Primary objectives were ORR per RECIST v1.1 for each cohort and higher programmed death ligand‐1 (PD‐L1) tumor expression. The relationship between PD‐L1 expression (measured as combined positive score [CPS]) and ORR was assessed. Twenty‐one Japanese patients (cohort A, n = 19; cohort B, n = 2) were treated. The median (range) age was 57 (37‐78) years; 19 (90.5%) patients had ECOG status of 0 and 16 (76.2%) patients had stage III‐IV disease. ORR was 19.0% (95% CI, 5.4‐41.9) and seemed to increase with increasing PD‐L1 expression. A total of 13 (61.9%) patients had treatment‐related adverse events (TRAE), and 5 (23.8%) had grade 3‐4 TRAE. There were no treatment‐related deaths in this subpopulation. Pembrolizumab monotherapy was associated with antitumor activity in Japanese patients with ROC, with no new safety signals identified in this subpopulation. The data suggested a trend toward higher PD‐L1 expression among some patients with higher ORR.