A Phase 2 Study of the IDO Inhibitor Epacadostat Versus Tamoxifen for Subjects With Biochemical-recurrent-only EOC, PPC or FTC Following Complete Remission With First-line Chemotherapy

Inclusion Criteria: * Subjects who have received first-line chemotherapy, which must have been a platinum-containing regimen. * Subjects who received maintenance paclitaxel or, bevacizumab, or alternative maintenance therapy (e.g. vaccines) are eligible for enrollment provided they have discontinued therapy at least 4 weeks for prior taxane and, at least 8 weeks for bevacizumab, or received medical monitor approval for time lapse from alternative maintenance therapy prior to randomization and recovered from toxicities to less than Grade 2. * Subject must be currently in remission by clinical and radiological criteria (Response Evaluation Criteria for Solid Tumors \[RECIST 1.1\]). a. If a PET scan or high-resolution CT scan is performed and demonstrates new disease \</= 1 cm, these subjects would be eligible. * Clinical remission is defined as: asymptomatic and a negative physical examination. * Scans are required post completion of platinum-containing therapy to document disease remission. * Prior to the first-line regimen, CA 125 must have been elevated at first diagnosis, must have normalized with the first-line therapy/regimen, and is currently elevated: a. CA 125 elevation is defined as 2 consecutive measurements that are both above the Upper Limit of Normal (ULN) at least 42 weeks apart, with the second measure showing further increases from the first measurement 1. If CA 125 is ≥ 2 × ULN the confirmatory value only needs to be 1 week apart. 2. CA 125 elevation is defined as a value that is at least 2 × ULN on 2 occasions at least 1 week apart (UK ONLY REQUIREMENT). * CA 125 elevation must be at least 3 months from completion of first-line platinum-containing regimen. * Documentation of at least 1 normal CA 125 level at approximately 3 months during or following first line therapy is required. * Subjects must have available archived tumor tissue. * Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1. * Adequate renal, hepatic, and bone marrow function based on screening laboratory assessments. Exclusion Criteria: * Subjects with any evidence of new disease (\> 1 cm) including new ascites as confirmed by imaging. * Any other prior antitumor systemic therapy except for first-line chemotherapy associated with previous CA 125 normalization or maintenance paclitaxel, bevacizumab, or alternative maintenance therapy as approved by the medical monitor. * Subjects with prior radiotherapy within 3 months of randomization and have not recovered from all radiotherapy-related toxicities, who have received radiation therapy to the chest within 3 months of randomization, or who have a history or radiation pneumonitis. * Subjects with protocol-specified active autoimmune processes except vitiligo or thyroiditis. * Subjects receiving investigational study drug for any indication, immunological-based treatment for any reason (except completed adjuvant therapy with medical monitor approval), or potent CYP3A4 inducers or inhibitors. * Subjects receiving monoamine oxidase inhibitors (MAOIs) within the 21 days prior to screening; subjects who have ever had Serotonin Syndrome (SS) after receiving 1 or more serotonergic drugs. * Subjects for whom tamoxifen therapy is contraindicated.