A Clinical Study of the Anti-cancer Effects of an Investigational Therapy or Chemotherapy in Patients With Recurring Uterine Cancer

Key Inclusion Criteria: * Are female adults (defined as ≥18 years of age or acceptable age according to local regulations at the time of voluntarily giving informed consent). * Have histologically confirmed endometrial cancer that: * Is recurrent, * Has a HER2 IHC score of 1+, 2+ (Cohort 1), or 3+ (Cohort 2) as determined by central laboratory testing for HER2 expression, and * Is not defined as a true sarcoma (i.e., leiomyosarcoma or endometrial stromal sarcoma). Note: Uterine carcinosarcoma is allowed. * Have measurable disease defined by RECIST v1.1. * Have Eastern Cooperative Oncology Group (ECOG) Performance Status of 0, 1 or 2. * Have recurrent endometrial cancer and meet any of the following: * developed recurrence \<12 months from completing platinum-based chemotherapy given as adjuvant therapy for Stage I to III disease, or * developed recurrence after platinum-based chemotherapy in the recurrent/metastatic setting. * Have received prior ICI treatment (i.e., anti-programmed death 1/anti-programmed death-ligand 1) * Have a life expectancy of ≥12 weeks at screening. Key Exclusion Criteria: * Are ineligible for all options in the investigator's choice of chemotherapy arm, per local prescribing information and institutional guidelines (applicable to Cohort 1 only). * Have a history of small bowel obstruction requiring hospitalization within the past 3 months prior the first dose of study treatment. * Have an uncontrolled intercurrent illness that would lim…