This study is a single-center, bidirectional cohort study. It aims to include 35 elderly (≥65 years old) Luminal A type breast cancer patients with axillary lymph node metastasis after surgery as the research subjects. After signing the informed consent, the patients who meet the inclusion criteria will have their various clinical and pathological data collected (preoperative imaging examinations, clinical and pathological information of the patients, basic disease conditions and medication strategies, surgical records, postoperative planned treatment plans and actual treatment situations, etc.), and their real adjuvant treatment situations (whether chemotherapy, radiotherapy, endocrine therapy, targeted therapy, etc. were performed after surgery) will be followed up and recorded. At the same time, paraffin tissues of breast cancer and metastatic lymph nodes of the patients will be collected from the pathology department of our hospital for 21-gene assay, and the recurrence risk index of the primary lesion and metastatic lymph nodes will be obtained using the risk index calculation logic of Amoy Diagnostics Company. An assessment will be conducted every 12 months after surgery until disease recurrence. After disease recurrence, survival follow-up will be conducted every three months until the patient's death. The predictive value of 21-gene assay for patient survival and whether chemotherapy is beneficial will be evaluated based on the follow-up data of the patients.

Inclusion Criteria:

• Sign a written informed consent；

• Female, age ≥ 65 years old；

• Patients who have undergone radical surgery for breast cancer (radical surgery refers to modified radical mastectomy, radical mastectomy or simple mastectomy + axillary lymph node dissection), and have been histologically confirmed to have axillary lymph node metastasis after surgery；

• Postoperative immunohistochemical typing and pTNM staging meet the following criteria:

  1. Luminal A type (ER and PR positive with a positive rate ≥ 20%, Her-2 gene negative, Ki67 < 15%), with pTNM staging of pTanyNanyM0.
  2. Or Luminal B, Her-2 gene negative type, with ER and PR positive and a positive rate ≥ 20%, Ki67 ≤ 30%, and pTNM staging of pTanyN1M0.
  3. Or age ≥ 70 years old, Luminal B, Her-2 gene negative type, with ER and PR positive and a positive rate ≥ 20%, Ki67 ≤ 30%, and pTNM staging of pTanyNanyM0.
  4. Or age ≥ 70 years old, but refuse or are unable to tolerate chemotherapy treatment, ER or PR positive, with pTNM staging of pTanyNanyM0；

• ECOG score 0-1；

• Expected survival time > 6 months.

Exclusion Criteria:

• Patients who have received preoperative neoadjuvant therapy in the past;
• Patients with bilateral breast cancer;
• Patients whose paraffin tissue specimens have been stored for more than 3 years at the start of the project;
• Patients with mental disorders who are unable to cooperate with subsequent treatment and follow-up;
• Patients with a history or evidence of disease, treatment or abnormal laboratory test values that may interfere with the trial results or prevent full participation in the study, or other situations deemed unsuitable for inclusion by the researcher, or those considered to have other potential risks and thus not suitable for participation in this study.

Qilu hospital of Shandong University or its medical alliance hospital