A Phase 2 Open-Label, Multicenter Study to Evaluate Efficacy and Safety of ZN-c3 in Adult Women with Recurrent or Persistent Uterine Serous Carcinoma

INCLUSION CRITERIA 1. Females ≥18 years of age at the time of informed consent. 2. Histologically confirmed recurrent or persistent USC for which no other proven effective treatment options are available or any available standard of care therapy was not tolerated or was refused by the subject. - Subjects with endometrial carcinoma of mixed histology where the serous component comprises at least 5% of the tumor will be considered eligible. - Subjects with carcinosarcomas (even if there is a serous component) are not eligible. 3. Measurable disease per RECIST Guideline Version 1.1 4. Required prior therapy for endometrial cancer: 1. Treatment with a platinum-based chemotherapy regimen. 2. Treatment with a PD-(L)1 inhibitor 3. Known HER2-positive tumors: Treatment with at least 1 HER2-targeted therapy, except for subjects who are not clinically eligible. 5. Adequate hematologic and organ function EXCLUSION CRITERIA 1. Any of the following treatment interventions within the specified time frame prior to C1D1: 1. Major surgery within 28 days 2. Any chemotherapy or targeted tumor therapy within 14 days or 5 half-lives (whichever is shorter). 3. Radiation therapy within 21 days; 4. Autologous or allogeneic stem cell transplant within 3 months. 5. Current use of any other investigational drug therapy <28 days or 5 half-lives (whichever is shorter). 2. Prior therapy with ZN-c3 or any other WEE1 inhibitor, ATR inhibitor, or CHK1/2 inhibitor for USC. 3. A serious illness or medical condition(s) including, but not limited to: Any evidence of bowel obstruction as determined by air/fluid levels on computed tomography (CT) scan, recent hospitalization for bowel obstruction within 3 months prior to C1D1, or recurrent paracentesis or thoracentesis within 6 weeks prior to C1D1.