Pembrolizumab in Treating Participants With Recurrent Ovarian Cancer

PRIMARY OBJECTIVES: I. To evaluate clinical anti-tumor activity of pembrolizumab monotherapy based on objective response rate (ORR) as assessed by the investigator per immune related Response Evaluation Criteria in Solid Tumors (irRECIST) in patients with recurrent ovarian cancer (ROC) whose tumors show an immunoreactive gene expression signature. SECONDARY OBJECTIVES: I. To evaluate clinical anti-tumor activity of pembrolizumab monotherapy based on progression-free survival (PFS) as assessed by the investigator per irRECIST in patients with ROC whose tumors show an immunoreactive gene expression signature. II. To evaluate clinical anti-tumor activity of pembrolizumab monotherapy based on PFS rate at 6, 12 and 18 months as assessed by the investigator per irRECIST in patients with ROC whose tumors show an immunoreactive gene expression signature. III. To evaluate and characterize the tolerability and safety profile of the study population after being treated with pembrolizumab as monotherapy. EXPLORATORY OBJECTIVES: I. To assess correlations of the immunoreactive gene signature with the validated a PD-L1 immunohistochemistry (IHC) assay using Merck's proprietary 22C3 antibody and the clinical activity observed in the study population. OUTLINE: Participants receive pembrolizumab intravenously (IV) on day 1. Courses repeat every 3 weeks for up to 35 courses (2 years) in the absence of disease progression or unacceptable toxicity. After completion of study treatment, participants are followed up at 30 and then every 9 and 12 weeks thereafter.