Breast cancer is a relatively common malignancy in women, and in a very small number of men may also have breast cancer. There is a form of treatment for breast cancer called targeted drug therapy, and the main drug used is Herceptin, also known as trastuzumab. It is a drug that can target the target of breast cancer with relatively few side effects, more precise action and better anti-tumor effect. It can be used in combination with chemotherapy, in addition to single agent, to prevent local recurrence and distant metastasis, and to prolong the survival of patients. For patients with advanced inoperable disease, Herceptin can be used if immunohistochemistry indicates HER2 overexpression, which refers to human epidermal growth factor receptor-2, and genetic testing is required to determine whether Herceptin can be used.