A Phase 1b/2, Open-Label, Multicohort Study of Disitamab Vedotin in Adults With HER2 Expressing Advanced Breast Cancer

The purpose of this clinical study is to learn about the safety and effects of the study medicine (called disitamab vedotin) for the possible treatment of people with breast cancer that is hard to treat and has spread in the body (advanced cancer).

This study is seeking participants who:

• have breast cancer that is hard to treat and has spread in the body (advanced cancer)
• have tumors that have HER2 on them
• have received previous treatment for their advanced breast cancer

All participants in this study will receive disitamab vedotin at the study clinic once every 2 weeks as an intravenous (IV) infusion (given directly into a vein).

Participants will take the study medicine until they or their doctor decides to stop. This might be because their cancer is getting worse, the study medicine is no longer helping, they have bad side effects, or they wish to stop taking the study medicine. During this time, the participants will have study visits every 2 weeks. After the participants have stopped taking the study medicine, they will have follow-up visits about every 6 weeks unless their cancer gets worse. After that, they will have follow-up phone calls about every 12 weeks.

The study team will look at the experiences of people receiving the study medicine. This will help the study team decide if the study medicine is safe and effective.