A Study to Evaluate the Pharmacokinetics, Efficacy, and Safety of HLX319 vs. EU-Phesgo® in the Neoadjuvant Therapy of HER2-Positive Early or Locally Advanced Breast Cancer

Inclusion Criteria:

* Voluntary participation in the clinical study and signed the Informed Consent Form (ICF).
* Male or female aged ≥ 18 years old at the time of signing the ICF;
* Histologically confirmed invasive breast cancer, stage II-IIIC, Human Epidermal Growth Factor Receptor 2 (HER2) positive confirmed by central laboratory.
* Participants agree to undergo surgery while meeting the criteria for surgery after neoadjuvant therapy.
* Left ventricular ejection fraction (LVEF) at baseline ≥ 55%.
* An Eastern Cooperative Oncology Group (ECOG) performance status (PS) score of 0-1.
* Adequate major organ functions.
* Women with child-bearing potential have a negative result of serum pregnancy test at screening period (within 7 days prior to the first dose) or if they are infertile, non- lactating, reproduction-age men and women following highly effective contraceptive measures until 7 months after last dose.

Exclusion Criteria:

* Stage IV breast cancer, bilateral breast cancer, or multicentric breast cancer.
* History of other malignancy within 5 years.
* Prior systemic therapy for breast cancer treatment or radiotherapy.
* Patients with a history of ductal carcinoma in situ (DCIS) or lobular carcinoma in situ (LCIS) who have received systemic therapy or radiotherapy to the ipsilateral breast.
* Patients who have undergone excision biopsy of the primary tumor and/or axillary lymph nodes or lymph node dissection.
* Have severe heart disease or medical conditions.
* Participants with viral hepatitis or those with autoimmune hepatitis, sclerosing cholangitis, or liver cirrhosis.
* Human Immunodeficiency Virus (HIV) infection, HIV antibody positive.
* Daily use of corticosteroid treatment is required.
* Sensitivity to any study medications or any of its ingredients or excipients.
* Participants who underwent any major surgery within 28 days prior to the first dose. Or participants who have received local radiotherapy, radiofrequency ablation, or interventional therapy within 2 weeks prior to the first dose.
* Received another interventional clinical trial therapy within 4 weeks prior to enrollment in the study, or intentionally participated in another interventional clinical trial during the entire study period.
* Severe, uncontrolled systemic diseases that may currently interfere with the therapeutic plan.
* Any other conditions which are inappropriate for the study in the opinion of the investigator.