The 21-gene test for breast cancer includes 16 tumor-related genes and 5 reference genes. Based on the results of these genetic tests, a risk score for breast cancer recurrence can be derived, which is divided into high risk, moderate risk and low risk. Then, with reference to the patient’s age, clinical stage, hormone receptor status, lymph node metastasis, etc., a comprehensive assessment is made to determine whether the patient needs chemotherapy or not. If the patient belongs to the low risk group, chemotherapy can be dispensed with and the patient’s pain is minimal and the impact on prognosis is not significant. The 21-gene test for breast cancer is very important in determining patient prognosis and predicting recurrence, and is now being used more and more widely in clinical practice.