Pembrolizumab in Patients With Advanced Clear Cell Gynecological Cancer

ImportanceAdvanced clear cell gynecological cancers (CCGCs) have a poor prognosis, with response rates to second-line chemotherapy less than 8%. Preliminary clinical activity with programmed cell death 1 protein (PD-1) inhibitors reported in CCGC merits further investigation.ObjectiveTo assess the clinical benefit of pembrolizumab in patients with previously treated advanced CCGC.Design, Setting, and ParticipantsThe PEACOCC trial is a single-arm multicenter phase 2 trial conducted at 5 UK centers investigating the clinical benefit and safety of pembrolizumab. PD-1 inhibitor–naive patients with histologically confirmed advanced CCGC, radiological disease progression following 1 or more prior courses of chemotherapy, and an Eastern Cooperative Oncology Group (ECOG) performance status (PS) score of 0 to 1 were included. Patients were enrolled from March 2019 to October 2021, with data collected until July 2024.InterventionsPembrolizumab, 200 mg, intravenously every 21 days up to 2 years until progression, discontinuation due to toxic effects, or patient/clinician decision. Up to 1 year of retreatment on diseases progression, if stable disease, partial response, or complete response at 2 years.Main Outcomes and MeasuresThe primary end point was progression-free survival (PFS) rate at 12 weeks using Response Evaluation Criteria in Solid Tumors version 1.1 to detect a 12-week PFS rate of 33% or greater and exclude a PFS rate of less than 15%, with 90% power and 1-sided 5% significance level. Secondary end points included objective response rate, duration of response, PFS, overall survival, safety, and quality of life.ResultsA total of 48 patients were eligible. The median (range) age was 58.5 (32-77) years, and 26 (54%) had an ECOG PS score of 0 and 22 (46%) had an ECOG PS score of 1; 41 (85%) had ovarian, 6 (13%) had endometrial, and 1 (2%) had cervical advanced CCGC. The median (range) courses prior therapy was 3 (1-6); 19 patients (40%) received prior anti-angiogenic therapy, and 19 (40%) had a platinum-free interval of more than 12 months. Grade 3 treatment-related adverse events were observed in 9 patients (19%), and no patients had grade 4 or 5 adverse events. A total of 45 of 46 patients (98%) had mismatch repair–proficient tumors. The 12-week PFS rate was 42% (95% CI, 28-57), and the best objective response rate was 25% (95% CI, 14-40), with 12 partial responses. After a median follow-up of 46.9 months (95% CI, 43.4-55.0), the median PFS was 2.7 months (95% CI, 1.3-5.4), and the median overall survival was 14.8 months (95% CI, 6.7-28.2).Conclusions and RelevanceThe PEACOCC trial showed clinical benefit with pembrolizumab in patients with previously treated advanced CCGC, of whom all except 1 had MMR-proficient disease. Clinical outcomes were durable with an overall tolerable safety profile, justifying further evaluation of pembrolizumab monotherapy for advanced CCGC in a randomized clinical trial.Trial RegistrationClinicalTrials.gov Identifier: NCT03425565