This is a phase II trial evaluating the efficacy and safety of SHR-A1811 monotherapy or combined with pyrotinib maleate in Stage II-III HER2-positive breast cancer. Subjects will receive the neoadjuvant therapy of SHR-A1811 monotherapy or combined with pyrotinib for six cycles, and then undergo surgery within 4 weeks after neoadjuvant therapy. Efficacy will be assessed every 2 cycles.

Inclusion Criteria:

• Female patients aged ≥ 18 but ≤ 75 years
• Histologically confirmed to be HER2-positive invasive breast cancer
• Treatment-naive patients with stage II-III
• Eastern Cooperative Oncology Group (ECOG) score 0-1
• Good level of organ function

Exclusion Criteria:

• Previously received any anti-tumor therapy (chemotherapy, radiotherapy, molecular targeted therapy, endocrine therapy, etc.)
• Received any other anti-tumor therapy at the same time
• Bilateral breast cancer, inflammatory breast cancer or occult breast cancer
• Stage IV breast cancer
• With a history of any malignancies in the past 5 years, excluding cured cervical carcinoma in situ and melanoma skin cancer
• Inability to swallow, chronic diarrhea, intestinal obstruction, and a variety of factors affecting drug administration and absorption
• Participated in other drug clinical trials within 4 weeks before enrollment
• History of allergies to the drug components of this protocol
• Clinically significant pulmonary diseases
• Clinically significant cardiovascular diseases
• History of immunodeficiency
• Active hepatitis and liver cirrhosis