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.

Trastuzumab IV infusion in 3-week cycles. Neoadjuvant treatment: 8 milligrams per kilogram (mg/kg) loading dose for Cycle 1, followed by 6 mg/kg for Cycles 2-4.

QL1209 IV infusion in 3-week cycles. Prior to surgery (neoadjuvant treatment): 840 milligrams (mg) loading dose for Cycle 1, followed by 420 mg for Cycles 2-4.

Pertuzumab IV infusion in 3-week cycles. Prior to surgery (neoadjuvant treatment): 840 milligrams (mg) loading dose for Cycle 1, followed by 420 mg for Cycles 2-4.

Docetaxel IV infusion in 3-week cycles. Neoadjuvant treatment: 75 mg/m2 for Cycles 1-4

All participants who are eligible for surgery will undergo surgery and have their pathologic response evaluated.