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

The study is divided into two cohorts (Cohort 1 and Cohort 2), to which participants will be enrolled based on the amount of human epidermal growth factor receptor 2 (HER2) in their tumor sample. In Cohort 1, the main goal is to assess how well BNT323 (also known as DB-1303) or chemotherapy (doxorubicin or paclitaxel \[or docetaxel, if participants cannot take paclitaxel\]) works by determining the progression-free survival (PFS) of participants who have been previously treated with immune checkpoint inhibitors (ICIs). In Cohort 2, the main goal is to assess how well BNT323 works by determining the objective response rate (ORR), that is, the percentage of participants whose tumor shrinks (partial response) or disappears (complete response) after treatment. The safety of BNT323 will also be assessed by following the occurrence of unfavorable/adverse effects that are seen after treatment. Other measures include the pharmacokinetics of BNT323 (or how BNT323 moves through and out of the body), the body's immune response, and the impact on quality of life.

• Cohort 1: PFS assessed by blinded independent central review (BICR) in participants with HER2 IHC 1+/2+ recurrent endometrial cancer
• Cohort 2: ORR assessed by BICR in participants with HER2 IHC 3+ recurrent endometrial cancer

1. Study completion expected

   Nov 2029

2. Primary completion expected

   Mar 2028

3. Last registry update

   16 Oct 2026

4. Started

   10 Jun 2025

5. Registered

   1 Apr 2024