Testing Whether the Combination of Two Immunotherapy Drugs Have Activity in Recurrent or Persistent Clear Cell Ovarian Cancer

PRIMARY OBJECTIVE: I. To assess the objective tumor response (proportion of objective response by Response Evaluation Criteria in Solid Tumors \[RECIST\] 1.1 criteria) of the combination of pembrolizumab (MK-3475 \[pembrolizumab\]) and epacadostat in patients with recurrent or persistent clear cell carcinoma of the ovary. SECONDARY OBJECTIVES: I. To determine the nature and degree of toxicity of MK-3475 (pembrolizumab) + epacadostat as assessed by Common Terminology Criteria for Adverse Events (CTCAE) in patients with recurrent or persistent clear cell carcinoma of the ovary. II. To estimate the progression-free survival (PFS) and overall survival (OS) in patients treated with combination of MK-3475 (pembrolizumab) and epacadostat. EXPLORATORY TRANSLATIONAL OBJECTIVES: I. Determine whether the ratio of plasma tryptophan to kynurenine (T:K) correlates with response to MK-3475 (pembrolizumab) + epacadostat, by evaluating plasma T:K pre-treatment, during treatment, and at disease progression. II. Determine whether the presence of PD-L1, IDO-1, tumor-infiltrating regulatory T cells (Tregs), CD8 tumor-infiltrating lymphocytes (TILs), and human leukocyte antigen (HLA) class I in the tumor microenvironment at baseline correlates with objective response to MK-3475 (pembrolizumab) + epacadostat. III. Determine whether soluble PD-L1 (sPD-L1) levels in plasma are correlated with response to MK-3475 (pembrolizumab) + epacadostat, by evaluating sPD-L1 concentrations pre-treatment, during treatment, and at disease progression. OUTLINE: Patients receive epacadostat orally (PO) twice daily (BID) and pembrolizumab intravenously (IV) over 30 minutes once every 3 weeks (Q3W). Cycles repeat every 21 days in the absence of disease progression or unacceptable toxicity. After completion of study treatment, patients are followed up every 3 months for 2 years, then every 6 months for 3 years, and annually thereafter.