The 21-gene test is usually referred to as the 21-gene test for breast cancer, also known as the 21-gene marker, which is an examination of the relevant genes and reference genes of breast cancer to determine the characteristics of the tumor and also to guide the subsequent treatment. 1. Determining the characteristics of the tumor For example, the BRCA1 gene, which is hereditary, is an important test in the 21-gene test; 2. The 21-gene test can provide clinicians with guidance on whether the patient is suitable for targeted therapy or immunotherapy. With the continuous improvement of breast cancer treatment technology and therapeutic drugs, 21-gene test plays an increasingly important role in the treatment of breast cancer. If conditions allow, patients are recommended to have 21-gene testing to improve the overall outcome of tumor treatment. Genetic testing is also not mandatory. If patients do not undergo this test, doctors can also make empirical judgments about patients’ treatment plans before, during and after surgery based on clinical experience, which usually leads to better treatment outcomes. Whether or not genetic testing is chosen, early detection and treatment are still advocated in the treatment of breast cancer.