We are doing this study to find out if an experimental drug called zelenectide pevedotin (the study drug) is a safe and effective option for people with breast cancer.

Breast Cancer

Adults ages 18+ who:

• Are diagnosed with either triple-negative breast cancer or HR+/HER2- breast cancer
• Have disease that is either unresectable (cannot be removed with surgery) or metastatic (has spread)
• Have confirmed NECTIN4 gene amplification
• Have never been treated with an antibody-drug conjugate that contains monomethyl auristatin E (vedotin)

For more information, contact the study team at breastcl@dm.duke.edu.

If you choose to join this study, you will go through a 28-day screening period to make sure that you are eligible to join. The screening period will include:

• Physical exams
• Blood draws
• Heart scans (echocardiograms and EKG)
• Imaging scans (CT, MRI, DEXA, PET/CT)

If you are found to be eligible, you will proceed to the study drug dosing period. During the dosing period, you will get the study drug over the course of 21-day periods called "cycles." You will get the study drug on days 1 and 8 of each cycle. The number of cycles you do will depend on how your body responds to the study drug. You will take the study drug for as long as you and the study doctor believe that you are getting a positive benefit.

You gill get the study drug as an intravenous (IV) infusion into a vein in your arm. Each dose takes about 60 minutes to give.

After you stop taking the study drug, you will come in for a physical exam about 30 days after your last dose. After this visit, you will continue to see the study doctor every 3 months for check-ups to see how you are doing.