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

This is an open-label, randomized, multi-site, Phase III, interventional clinical study designed to determine the efficacy and safety of BNT323 compared with investigator's choice of single agent chemotherapy in previously treated participants with recurrent endometrial cancer (including HER2 1+ or 2+ score as determined using a centralized immunohistochemistry \[IHC\] analysis method), whose disease has progressed on at least one line of platinum-based therapy and ICI (Cohort 1). In addition, participants with recurrent endometrial cancer with HER2 IHC 3+ score will be enrolled in a BNT323 monotherapy arm (Cohort 2) to further investigate the efficacy and safety of BNT323. In Cohort 1, participants will be randomized 2:1 to receive either BNT323/DB-1303 or investigator's choice of single agent chemotherapy, preferably doxorubicin or paclitaxel (or docetaxel if contraindicated to paclitaxel and available at the site) until Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST v1.1) defined progressive disease (PD) unless there is unacceptable toxicity, withdrawal of consent, or another criterion for discontinuation is met. In Cohort 2, participants will receive BNT323 monotherapy until RECIST v1.1 defined PD unless there is unacceptable toxicity, withdrawal of consent, or another criterion for discontinuation is met. The study consists of a screening period, a treatment period, a safety follow-up period, an efficacy follow-up period, and a long-term survival follow-up. The expected treatment duration per participant is \~6 months, followed by an anticipated long-term survival follow-up period of up to 53 months.