Study in Participants With Early-Stage or Locally Advanced Human Epidermal Growth Factor Receptor (HER) 2-Positive and Estrogen Receptor/Progesterone Receptor Negative Breast Cancer to Evaluate the Efficiency and Safety of Treatment With Trastuzumab Plus (+) QL1209/Pertuzumab + Docetaxel.

This is A multi-center, randomized, double-blind, parallel control，comparative clinical trial.

The primary objective is to evaluate whether the clinical efficacy of QL1209 and pertuzumab are similar in patients with early-stage or locally advanced HER2-positive and estrogen receptor/progesterone receptor negative breast cancer.

The secondary objective are to evaluate whether the clinical safety and immunogenicity of QL1209 and pertuzumab are similar in patients with early-stage or locally advanced HER2-positive and estrogen receptor/progesterone receptor negative breast cancer.

Inclusion criteria

• Volunteer to participate in this clinical study; Completely understand and know this study as well as sign the informed consent form (ICF);
• Age ≥ 18 years and ≤ 80 years when ICF is signed;
• Histologically confirmed invasive breast carcinoma with a primary tumor size of more than (>) 2 centimeters (cm) by standard local assessment technique; Breast cancer stage at presentation: early-stage (T2-3, N0-1, M0) or locally advanced (T2-3, N2 or N3, M0; T4, any N, M0); HER2-positive breast cancer confirmed by immunohistochemistry or HER2 gene amplification by in situ hybridization; Estrogen receptor and Progesterone receptor negative.
• Eastern Cooperative Oncology Group Performance Status equal to or less than (<=) 1.
• Baseline left ventricular ejection fracture >= 55% measured by echocardiography (preferred) or multiple gated acquisition scan

Exclusion criteria

• Stage IV metastatic breast cancer;
• Inflammatory breast cancer;
• Previous anti-cancer therapy or radiotherapy for any malignancy;
• History of malignancies other than colorectal cancer within 5 years prior to randomization, excluding cutaneous basal cell carcinoma, cervical carcinoma in situ, and thyroid papillary adenocarcinoma of non-melanoma after radical treatment;
• Concurrent anti-cancer treatment in another investigational trial, including hormone therapy, bisphosphonate therapy, or immunotherapy;
• Major surgical procedure within 4 weeks prior to randomization or from which the participant has not fully recovered;
• Serious cardiac illness or medical condition;
• Other concurrent serious diseases that may interfere with planned treatment, including severe pulmonary conditions/illness;
• Sensitivity to any of the study medications, any of the ingredients or excipients of these medications, or benzyl alcohol;
• Pregnant or lactating