A Clinical Trial to Test if the Investigational Drug BNT329 is Safe and Potentially Beneficial for People With Advanced Solid Tumors Known to Express the Tumor Marker CA19-9

The study will consist of up to four parts (Parts A, B, C, and D). Parts A and B will be a dose escalation to investigate the safety and tolerability of BNT329. Parts A and B will enroll participants with the following advanced solid tumors known to express carbohydrate antigen 19-9 (CA19-9): pancreatic ductal adenocarcinoma (PDAC) (the most common type of pancreatic cancer), bile duct cancer, a certain type of bladder cancer that started in the lining of the bladder or urinary tract (invasive urothelial carcinoma of the bladder and urinary tract), colorectal cancer, gastroesophageal junction cancer, gastric adenocarcinoma, endometrial cancer, or ovarian cancer. The cancer must not have responded well to previous treatments. The study will start with recruitment into Part A. Part B (testing a more frequent dosing schedule) will only be opened if indicated by cumulative data from Part A of the study. Part C (testing pre-dosing with a CA19-9 targeting monoclonal antibody prior to BNT329 administration) will only be opened in case of unforeseen safety and/or weak efficacy signals are detected in Part A and (if opened) Part B. Details on Part C will be added in a future update, if it is necessary, to open this part. Part D will be a dose optimization and proof-of-concept study to further investigate the safety and tolerability of BNT329 and to investigate preliminary anti-tumor activity. Part D will enroll participants with second-line plus PDAC. Parts A, B, and C will be non-randomized. In Part D, participants will be randomized (1:1) into one of two arms which will evaluate two dose levels (as selected from Parts A and B). The study consists of a screening period, a treatment period, an end of treatment visit, two safety follow-up visits, and a survival follow-up period. The treatment period will last for a maximum of 2 years. Participants will remain in the survival follow-up until death, withdrawal of participant's consent, or termination of the study, whichever occurs first.