**Study Purpose:** This study aims to test the safety and effectiveness of a drug called INCB123667 for people with a type of ovarian cancer that does not respond to platinum-based treatments. This cancer is linked to high levels of a protein called Cyclin E1.

**Eligibility:** Participants must have a specific type of ovarian cancer, called high-grade serous epithelial cancer, and should have tried between 1 to 4 previous treatments. They need a biopsy to check the tumor, which can be a new sample or one taken in the last 5 years. Participants should have tried a drug called bevacizumab, unless advised against it by a doctor. If their tumor tests positive for a specific marker called FRα, they must have received another drug named mirvetuximab soravtansine, unless there's a medical reason not to.

• **Study Duration:** The study involves ongoing treatments and assessments; the exact length is not specified.
• **Participating:** Be prepared for possible new biopsies and medical evaluations.
• **Risks and Benefits:** The study checks how well the drug works and its safety, so there may be unknown risks.