A Clinical Study of the Anti-cancer Effects of an Investigational Therapy or Chemotherapy in Patients With Recurring Uterine Cancer (Fern-EC-01)

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+, or 3+ as determined by central laboratory testing for HER2 protein 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 1.1.

• Have Eastern Cooperative Oncology Group (ECOG) Performance Status of 0, 1 or 2.

• Have had at least one prior line of platinum-based therapy (in any setting). Up to three lines of prior therapy are allowed. Prior hormonal therapy and radiation are allowed and do not count as prior lines of therapy. Platinum-based chemotherapy and ICI may have been given together or in separate lines of therapy.

• Have a life expectancy of ≥12 weeks at screening.

Key Exclusion Criteria:

• Ineligible for all options in the investigator's choice of chemotherapy arm. Participants with contraindications to paclitaxel and doxorubicin treatment, per local prescribing information and institutional guidelines, cannot be enrolled to the study.
• Have a history of small bowel obstruction requiring hospitalization within the past 3 months prior to randomization.
• Have an uncontrolled intercurrent illness that would limit compliance with study requirement or substantially increase risk of incurring adverse events (AEs).
• Have clinically uncontrolled pleural effusion, ascites or pericardial effusion requiring drainage, peritoneal shunt, or cell-free concentrated ascites reinfusion therapy within 2 weeks prior to randomization.
• Have a history of (non-infectious) interstitial lung disease (ILD)/pneumonitis that required steroids, have current ILD/pneumonitis, or where suspected ILD/pneumonitis cannot be ruled out by imaging at screening.
• Participants with prior use of immunosuppressive medication within 14 days prior to first dose of study treatment, except for intranasal and inhaled corticosteroids or systemic corticosteroids at doses of less than 10 mg/day of prednisone or equivalent, and topical corticosteroids. Participants receiving corticosteroids may continue if the dose is stable upon giving informed consent.
• Have a lung-specific intercurrent clinically significant illness including, but not limited to, any underlying pulmonary disorder (e.g., pulmonary emboli within 3 months prior to study randomization, severe asthma, severe chronic obstructive pulmonary disorder, restrictive lung disease, pulmonary fibrosis, radiation pneumonitis, significant pleural effusion etc.), and any autoimmune, connective tissue or inflammatory disorder with pulmonary involvement (i.e., rheumatoid arthritis, Sjogren's syndrome, sarcoidosis etc.), and/or prior pneumonectomy (complete).
• Have uncontrolled infection requiring systemic antibiotics, antivirals, or antifungals within 2 weeks prior to randomization.
• Have unresolved toxicities from previous anti-cancer therapy, defined as toxicities (other than alopecia) not yet resolved to Grade ≤1 or baseline.
• Are pregnant or breastfeeding or are planning pregnancy during the study or within 7 months after the last dose of study treatment.
• Have a history of allergies, hypersensitivities, or intolerance to the study treatments (investigational medicinal products and auxiliary medicinal product) including any excipients thereof or to other monoclonal antibodies.
• Had prior treatment with topoisomerase I inhibitors, including ADCs with exatecans.
• Have left ventricular ejection fraction (LVEF) <55% by either echocardiography (ECHO) or multiple-gated acquisition (MUGA) within 28 days before randomization. This includes participants with tissue doppler E/e' ratio >15.

NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.