In 2007, the American Society of Clinical Oncology (ASCO) announced that the Breast 21 Gene Test should be considered in breast cancer treatment planning for patients with estrogen receptor-positive, early-stage breast cancer without lymph node spread. The National Cancer Center System (NCCN) recommended the use of the 21-gene test for breast cancer in its 2008 breast cancer treatment guidelines. In the 2010 guideline, it was clearly stated that chemotherapy indication assessment for ER+/HER2- patients should be combined with the 21-gene test, and in the 2013 St. Gallen Conference consensus, chemotherapy is required for patients with high RS on the 21-gene test in Luminal A breast cancer. In 2015, the NCCN guidelines reinforced the value of the 21-gene test for breast cancer. It is clear that “21-gene testing for breast cancer” has become a hot topic in breast cancer research. However, most patients with breast disease are not familiar with this test, so this article is a brief introduction. I. What is “Breast 21 Gene Test”? The “Breast 21 Gene Test” is to detect the expression of a specific set of genes in malignant tumor tissues to provide information for predicting prognosis, recurrence, metastasis and even guiding treatment, with the ultimate goal of providing individualized treatment for patients. The project measured the expression levels of 21 genes in breast cancer tumor tissues, including 16 tumor-related genes and 5 reference genes. 16 tumor-related genes include Ki-67, STK15, Survivin, CyclinB1, MYBL2, invasion-related genes Stromelysin3 (MMP11), Cathepsin L2 (CTSL), and Stromelysin 2 (CTSL). Cathepsin L2 (CTSL2); Her-2-related genes GRB7, Her-2; hormone-related genes ER, PR, Bcl-2, SCUBE2; GSTM1; BAG1; CD68. 5 reference genes refer to β-actin (ACTB), GAPDH, RPLPO, GUS, TFRC. 21 Gene test results are expressed in the form of scores, which are used to make predictions about the possible biological behavior of the tumor, providing individualized prediction of treatment efficacy and 10-year risk of recurrence. II. Do all breast cancer patients need chemotherapy? Breast cancer has developed a comprehensive treatment model centered on surgery, with chemotherapy, radiotherapy and endocrine therapy as adjuvant. Among them, chemotherapy is the more effective treatment. However, not all patients need chemotherapy, and excessive chemotherapy may even aggravate the patient’s condition. So how do you know whether you should choose chemotherapy or not? The “Breast 21 Gene Test” is an effective tool to determine whether chemotherapy is needed or not Traditional pathological analysis is the basis for the assessment of the benefit of chemotherapy for breast cancer, but the assessment is limited. “It is the only multigene test jointly recommended by several authoritative medical institutions in the United States, which can accurately determine the benefit of chemotherapy and is an effective tool to assess whether chemotherapy is needed after surgery. The 21-gene test is a new method born in the genomic era, which can comprehensively describe the tumor status, effectively determine the benefit of chemotherapy, and assess the risk of recurrence. Based on the recurrence score (RS) obtained from the 21-gene test, patients are classified into three groups with low, intermediate, and high risk of recurrence: (1) RS <18, a low risk group with little benefit from chemotherapy, and endocrine therapy can be considered;< span=""> (2) RS between 18 and 30, an intermediate risk group, and additional chemotherapy can be considered based on other clinical indicators; (3) RS ≥ 31, a high risk group. (3) RS≥31, a high risk of recurrence group, with a greater benefit of chemotherapy, can be considered for clinical treatment accordingly. The 21-gene test has become widely used in clinical practice: In the United States, the 21-gene test has rapidly become the standard procedure for breast cancer treatment, and has been used by more than 7,500 physicians more than 65,000 times. To date, the test has been available in several countries in Europe and the United States for nearly 9 years, benefiting 150,000 people. In China, this technology has also started to be applied, and the test is jointly conducted by large hospitals and professional testing institutions, providing a strong guarantee for breast cancer treatment in China. Who needs the “Breast Cancer 21 Gene Test”? Patients with stage I or II, estrogen receptor positive, lymph node metastasis negative and newly diagnosed breast cancer to be treated with tamoxifen. Post-menopausal patients with lymph node positive, estrogen receptor positive invasive breast cancer can also be evaluated for chemotherapy with the 21-gene test. When should I undergo the 21-gene test for breast cancer? ”The 21-gene test should be performed after the patient has undergone surgery (mastectomy or mastectomy) and before the next treatment decision is made. ”The Breast 21 test is a non-invasive test that eliminates the need for any additional puncture procedures and uses tissue removed during the original surgery (mastectomy, mastectomy or core puncture biopsy).