A Prospective, Open-label, Randomized Trial Comparing Switch to A1811 Versus Continued THP Neoadjuvant Therapy After THP Induction in HER2-Positive Breast Cancer (SwithADC)

Inclusion Criteria:

- 1.18-75 years old 2.Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 3.HER2-positive breast cancer was defined by core needle biopsy pathology showing HER2 positivity, with IHC score of 3+ or IHC score 2+ with positive ISH results 4.At initial diagnosis, tumors were stage II-III according to the AJCC 8th edition breast cancer staging system and deemed operable 5.no prior history of any systemic anti-cancer therapy for breast cancer 6.Adequate organ function 7.Women of reproductive potential must have a negative pregnancy test prior to enrollment. Women of childbearing potential must commit to using effective contraception from study start until 6 months after the last dose of study medication, with ongoing assessment of adherence to contraception.

8.All participants must voluntarily participate in this study and provide written informed consent, with consent approved by the ethics committee prior to use

Exclusion Criteria:

- 1.Bilateral breast cancer, stage IV breast cancer, or inflammatory breast cancer; 2.Any history of malignancy within 5 years prior to signing informed consent, excluding treated cervical carcinoma in situ, non-melanoma skin cancer (basal cell carcinoma or squamous cell carcinoma) in remission; 3.Receiving anti-tumor therapy in another interventional clinical trial concurrently, including but not limited to chemotherapy, endocrine therapy, biologic therapy, bone-modifying agents, or immune checkpoint inhibitors; 4.Major surgery unrelated to breast cancer within 4 weeks prior to the first dose of study drug, or not yet fully recovered from such surgery; 5.Severe cardiac disease or unstable condition; 6.Uncontrolled active infections; history of immunodeficiency, including HIV-positive status, or other acquired or congenital immunodeficiency diseases, or a history of organ transplantation 7. Known hypersensitivity to any component of the study drug regimen; 8. Pregnant or breastfeeding women, women of reproductive potential with a positive baseline pregnancy test, or sexually active individuals not willing to use effective contraception from the time of enrollment through 6 months after the last study drug administration; 9.Known or suspected interstitial pneumonia; major or clinically significant pre-existing respiratory diseases within 3 months prior to first dose that could interfere with assessment of drug-related pulmonary toxicity or its management.

10.urrently participating in another interventional pharmacologic clinical study; 11. Refusal to comply with follow-up procedures; 12. Presence of other serious medical or psychiatric conditions or laboratory abnormalities that may increase the risk of participation, interfere with study results, or for any other reason lead the investigator to believe the subject is not suitable for participation in this study.