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.

Inclusion Criteria:

1. Volunteer to participate in this clinical study; Completely understand and know this study as well as sign the informed consent form (ICF);
2. Age ≥ 18 years and ≤ 80 years when ICF is signed;
3. 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.
4. Eastern Cooperative Oncology Group Performance Status equal to or less than (\<=) 1.
5. Baseline left ventricular ejection fracture \>= 55% measured by echocardiography (preferred) or multiple gated acquisition scan

Exclusion Criteria:

1. Stage IV metastatic breast cancer;
2. Inflammatory breast cancer;
3. Previous anti-cancer therapy or radiotherapy for any malignancy;
4. 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;
5. Concurrent anti-cancer treatment in another investigational trial, including hormone therapy, bisphosphonate therapy, or immunotherapy;
6. Major surgical procedure within 4 weeks prior to randomization or from which the participant has not fully recovered;
7. Serious cardiac illness or medical condition;
8. Other concurrent serious diseases that may interfere with planned treatment, including severe pulmonary conditions/illness;
9. Sensitivity to any of the study medications, any of the ingredients or excipients of these medications, or benzyl alcohol;
10. Pregnant or lactating