A Study of A166 in Patients With HER2-Positive Unresectable or Metastatic Breast Cancer

This study will evaluate the efficacy of A166 in patients with HER2-positive unresectable or metastatic breast cancer previously treated with TOP1 inhibitor Antibody-Drug Conjugates.

A166 will be administered every 3 weeks (Q3W) intravenous (IV) infusion.

Inclusion criteria

• Male or female patient ≥ 18 years and ≤ 75 years when signing the informed consent form.
• Breast cancer patients by histopathology and/or cytology documented.
• In the advanced or metastatic stage, having received no more than 5 lines of systemic therapy, one of which must include a HER2 ADC with a topoisomerase inhibitor payload.
• Patients must have experienced disease progression or intolerance during or after the most recent treatment prior to randomization.
• At least one measurable lesion according to RECIST 1.1 criteria.

Exclusion criteria

• Previous treatment with A166 or any HER2-targeted antibody-drug conjugate (ADC) with a microtubule inhibitor payload.
• Known history of severe hypersensitivity to other monoclonal antibodies, or allergy to A166 or their components.
• Permanent discontinuation of trastuzumab or its biosimilars due to any toxicity in prior treatments.
• Presence of severe corneal epithelial disease at baseline; or inability to perform daily activities without contact lenses.
• Presence of spinal cord compression or clinically active central nervous system (CNS) metastases.
• Other conditions considered by the investigator to make the patient unsuitable for participation in the study.