Study of Avelumab With or Without Entinostat in Participants With Advanced Epithelial Ovarian Cancer

The study is comprised of 2 phases: an open-label Safety Lead-in (Phase 1b) followed by an Expansion Phase (Phase 2). The Expansion Phase will evaluate the efficacy and safety of entinostat with avelumab when administered at the Recommended Phase 2 Dose (RP2D) versus avelumab alone in participants with advanced epithelial ovarian cancer in a randomized, double-blind, placebo-controlled setting. In Phase 2, participants will be randomized in a 2:1 ratio to receive avelumab plus entinostat or avelumab plus placebo, respectively. All participants will be assessed at Screening and at specified times during the conduct of the study using standard clinical and laboratory assessments. Participants will be assessed for response through radiological assessments. Participants will continue receiving their appropriate cycles of study treatment until tumor progression or adverse events (AEs) occur which necessitate discontinuing therapy as determined by the Investigator.