• Age ≥ 18 yrs old female patients who provide written informed consent for the study.
• Patients must have a confirmed diagnosis of high-grade serous ovarian cancer, primary peritoneal cancer, or fallopian tube cancer.
• Patients must have received prior standard of care of surgical intervention, including hysterectomy and salpingo-oophorectomy.
• Adequate organ function as determined by laboratory tests as defined below at screening.

• Patients with carcinosarcoma (malignant mixed Mullerian tumor), clear cell carcinoma, endometrioid carcinoma, low grade serous carcinoma, mucinous adenocarcinoma and ovarian cancer not otherwise specified.
• Patients with primary platinum-refractory disease, defined as disease that did not respond to (CR or PR), or has progressed within 3 months of the last dose of first-line platinum-containing chemotherapy.
• Patients who have active inflammatory bowel disease or intestinal obstruction.
• Patient who had an allogenic tissue/organ transplant or stem cell transplantation will be excluded.

All procedures to be conducted during the 35 cycles (approximately 2 years) of the treatment period will be performed according to the study schedule.

• The patient and/or the patient’s insurance company will be responsible for the medical costs that you would get as part if the study, just as you would if you were getting the usual care for your ovarian cancer.
• The patient will not be paid for taking part in this study. However, the patient may be eligible for assistance with costs associated with travel expenses with provided receipts. Please speak with your study coordinator or physician for details.

Compare two doses of ONC-392 in combination with a fixed dose of pembrolizumab in participants with ovarian cancer who are resistant to platinum-based chemotherapy.