Breast cancer 21 gene test low-risk patients need only endocrine therapy and may not need chemotherapy, which can do more harm than good. Breast cancer 21 gene test carries out recurrence risk score, i.e. RS score. The risk of breast cancer recurrence is assessed based on 21 breast cancer-related genes, including proliferation, invasion, HER2-related genes, hormone-related genes, etc., and the RS score is calculated according to a certain weighting, in which the RS score of <18 is considered as low-risk. In general, those with low risk of recurrence have a lower chance of recurrence, and those with low risk of recurrence are not likely to benefit from chemotherapy, but rather over-treatment and need to bear the side effects of chemotherapy. Therefore, chemotherapy is not recommended for those with low risk of recurrence, and only endocrine therapy is recommended. At present, the 21-gene test in China is not yet very standardized, and the decision of adjuvant chemotherapy based only on the 21-gene test results should be made with caution, and it is recommended that patients combine the results of pathological examinations and other results to make a comprehensive judgment and choose an appropriate treatment plan.