A Study of Onapristone ER Alone Or In Combination With Anastrozole in Gynecologic Cancers That Respond to Progesterone

Inclusion Criteria: * Histologically confirmed diagnosis at MSK of either (1) granulosa cell ovarian cancer, (2) low grade serous ovarian/ primary peritoneal cancer, or (3) endometrioid endometrial cancer; with PR expression ≥1% by IHC on archival tissue taken within the prior 3 years or new biopsy if no archival tissue is available. IHC results do not have to be from MSK. * Measurable disease as defined by RECIST 1.1. Measurable disease is defined as at least one lesion that can be accurately measured in at least one dimension. Each lesion must be ≥10mm when measured by CT or MRI. Lymph nodes must be ≥15mm in short axis when measured by CT or MRI * Patients must have had one prior chemotherapy regimen for management of disease. Note: additional lines of chemotherapy, biologic or immunotherapy are allowed. * Recovery from effects of recent surgery, radiotherapy, or chemotherapy * At least 4 weeks out from their last dose of radiation therapy * At least 4 weeks post-op from any major surgical procedure * At least 3 weeks out from their last dose of chemotherapy and/or biologic/targeted therapy * Must be ≥ 18 years of age * Karnofsky Performance Status (KPS) of ≥ 70% * Women of child-bearing potential must have a negative pregnancy test within 14 days prior to commencement of study treatment * Women of child bearing potential must use an effective form of contraception during study and for at least 6 months after completion of study treatment * Laboratory Test Findings perform…