A Study of A166 Versus Trastuzumab Emtansine (T-DM1) in Patients With HER2-Positive Unresectable or Metastatic Breast Cancer Previously Treated With Trastuzumab and Taxane Therapy

Prior treatment

• Previous treatment with A166 or any HER2-targeted antibody-drug conjugate (ADC) with a microtubule inhibitor payload.
• Permanent discontinuation of trastuzumab or its biosimilars due to any toxicity in prior treatments.

Other illness

• Known history of severe hypersensitivity to other monoclonal antibodies, or allergy to A166 , T-DM1 (trastuzumab emtansine) or their components.
• Presence of severe corneal epithelial disease at baseline; or inability to perform daily activities without contact lenses.
• Other conditions considered by the investigator to make the patient unsuitable for participation in the study

Other

• Presence of spinal cord compression or clinically active central nervous system (CNS) metastases.

• Male or female patient ≥ 18 years and ≤ 75 years when signing the informed consent form.
• Breast cancer patients by histopathology and/or cytology documented.
• Disease progression after receiving a trastuzumab-based regimen (or a commercially available trastuzumab biosimilar or inetetamab) in the advanced or metastatic setting, or disease progression/recurrence within 12 months during or after (neo)adjuvant therapy (with a trastuzumab-based regimen or commercially available trastuzumab biosimilar).
• Have previously received taxanes.
• 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