Human epidermal growth factor receptor 2 (HER2) positive breast cancer is a molecular subtype with high malignancy and high risk of recurrence and metastasis. 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 trastuzumab and paltuzumab are concentrated in the group of patients with positive lymph nodes. Can targeted therapy be used to reduce the progression of chemotherapy and further achieve efficient and low toxicity strategies. To explore the efficacy and safety of adjuvant therapy of taxane chemotherapy combined with trastuzumab targeting therapy for low-risk HER2 positive and lymph node negative early breast cancer.

Inclusion Criteria:

• 1) Treatment in Peking University People's Hospital for radical resection of breast cancer and had hospitalization records;
• 2) Postoperative pathology confirmed invasive breast cancer, and the pathological stage was T1a-b (T ≤ 1cm), N0, HER2 positive, with high-risk factors (G3, or hormone receptor negative); Or the pathological stage is T1c (1cm < T ≤ 2cm), N0, and there are no high-risk factors (G1/G2, hormone receptor positive);
• 3)Signed an agreement to participate in the PKUPH Breast Disease Cohort study at Peking University People's Hospital.

Exclusion Criteria:

• 1) Lack of clinical pathological data (such as imaging data, pathological data);
• 2) Preoperative neoadjuvant therapy;
• 3) Patients with metastatic breast cancer or bilateral breast cancer;
• 4) Failed to undergo curative surgery.

invasive breast cancer, and the pathological stage was T1a-b (T ≤ 1cm), N0, HER2 positive, with high-risk factors (G3, or hormone receptor negative); T1c (1cm < T ≤ 2cm), N0, and there are no high-risk factors (G1/G2, hormone receptor positive)