Human epidermal growth factor receptor 2 (HER2) positive breast cancer is a molecular subtype with high malignancy and easy recurrence and metastasis. The emergence of HER2 targeted drugs has greatly improved the prognosis and survival of such patients. At present, for HER2 positive breast cancer patients with negative lymph nodes, chemotherapy drugs combined with trastuzumab is the current standard treatment scheme, and in most cases, chemotherapy uses a combination of two drugs, while the main beneficiaries of the target treatment of trastuzumab and pertuzumab are concentrated in the group of patients with positive lymph nodes. Can the use of target therapy to de-escalation chemotherapy and further achieve a strategy of high efficacy and low toxicity. It is planned to explore the efficacy and safety of T1-T2, HER2 positive early breast cancer patients with negative lymph nodes to achieve chemotherapy reduction based on risk stratification.

Inclusion Criteria:

• 1) Treated in Peking University People's Hospital and underwent radical resection with hospitalization records;
• 2) Postoperative pathology confirmed invasive breast cancer, pathological staging was T2, N0, HER2 positive, and accompanied by one of the high-risk factors (G3, or hormone receptor negative);
• 3) Has signed and agreed to participate in the PKUPH breast disease cohort study.

Exclusion Criteria:

• 1) Lack of clinical and pathological data (such as imaging data and pathological data);
• 2) Preoperative neoadjuvant therapy;
• 3) Patients with metastatic breast cancer or bilateral breast cancer;
• 4) Failure to perform radical surgery.

invasive breast cancer, pathological staging was T2, N0, HER2 positive, and accompanied by one of the high-risk factors (G3, or hormone receptor negative)