Human epidermal growth factor receptor 2 (HER2) positive breast cancer is a molecular subtype with high malignancy and high risk to recurrence and metastasis. After the appearance of anti-HER2 targeted drugs, the prognosis and survival of these patients were greatly improved. In addition to trastuzumab and pertuzumab, the use of tyrosine kinase inhibitor (TKI) can further improve the survival. The evidence of previous adjuvant TKI anti-HER2 therapy was mainly from ExteNET study. However, due to the limitations of the times, ExteNET research is based on the background of only trastuzumab targeted therapy. Nowadays, there is no evidence that trastuzumab combined patuzumab,use of T-DM1, followed by sequential neratinib can still obtain absolute benefits. Therefore, there is no standard for the use of neratinib in current clinical practice. Investigators want to explore, in the real world, the efficacy and safety of sequential use of naratinib in adjuvant therapy.

Investigators retrospectively recuited patients with early HER2 positive breast cancer treated in Peking University People's Hospital center from January 1, 2019 to November 31, 2024, and prospectively recruit same patients from December 1, 2024 to December 31, 2028. To compare the efficacy and safety of sequential use of neratinib.

Inclusion Criteria:

1. Patients with HER2 positive breast cancer who were diagnosed by core needle biopsy/operation in Peking University People's hospital;
2. The patients were treated in Peking University People's Hospital and underwent radical resection with hospitalization records;
3. Received standard anti-HER2 neoadjuvant/adjuvant therapy (trastuzumab, trastuzumab combined with pertuzumab, T-DM1)
4. 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. Patients with metastatic breast cancer or bilateral breast cancer;
3. Failure to perform radical surgery

patients recieved Neratinib for 1 year or not.

Primary end point: 5-year invasive dieased free survival

Inclusion Criteria:

• 1) Patients with HER2 positive breast cancer who were diagnosed by core needle biopsy/operation in Peking University People's hospital;
• 2) The patients were treated in our hospital and underwent radical resection with hospitalization records;
• 3) Received standard anti-HER2 neoadjuvant/adjuvant therapy (trastuzumab, trastuzumab combined with pertuzumab, T-DM1)
• 4) 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) Patients with metastatic breast cancer or bilateral breast cancer;
• 3) Failure to perform radical surgery

Early stage HER2 positive breast cancer patients received radical surgery and standard neoadjuvant/adjuvant therapy