This is an open-lable, multicenter, and single arm phase II trial to evaluate treatment with KN026 plus docetaxel as neoadjuvant therapy in patients with early-stage (T1c or 2, N1, M0; T2 or 3, N0, M0) or locally advanced (T1c or 2 or 3, N2, M0; T3N1M0; T1c or 2 or 3, N3a or 3b, M0) HER2-positive breast cancer. The subjects will receive KN026 30 mg/kg IV + Docetaxel 75/m2 every 3 weeks for four cycles prior to surgery.

KN026 is an anti-HER2 bispecific antibody that can simultaneously bind two non-overlapping epitopes of HER2, leading to a dual HER2 signal blockade.

Inclusion Criteria:

• Male or female subject >= 18 years;
• Histologically or cytologically confirmed HER2-positive breast cancer defined as 3+ determined by validated IHC or positive by in situ hybridization (ISH);
• Early-stage (T1c or 2, N1, M0; T2 or 3, N0, M0) or locally advanced (T1c or 2 or 3, N2, M0; T3N1M0; T1c or 2 or 3, N3a or 3b, M0) breast cancer;
• Adequate organ function assessed within 7 days prior to first trial treatment;
• ECOG score 0 or 1;
• Left ventricular ejection fraction (LVEF) ≥ 55% at baseline;

Exclusion Criteria:

• Stage IV (metastatic) breast cancer;
• Inflammatory breast cancer;
• Previous anti-cancer therapy or radiotherapy for any malignancy;
• Major surgery for any reason within 28 days;
• History of uncontrolled intercurrent illness;
• Other medical conditions that at the discretion of investigator interfere with the requirements of the trial in terms of safety or efficacy evaluation, or treatment compliance;