Breast cancer is a disease with high morbidity and mortality among female malignant tumors, and its incidence rate has been in a rapid rise in the past three decades. According to experts from the Department of Oncology of Shanghai Center for Disease Control and Prevention, compared with the incidence rate of 17/100,000 in the early 1970s, the incidence rate of female breast cancer has more than tripled to nearly 60/100,000 at present. According to the 18.5 million people living in Shanghai last year, a conservative estimate shows that there are more than 5,000 new cases of breast cancer in Shanghai each year, and the number of patients who have developed the disease over the years is very impressive. At the end of last century, with the development of medical science, people have conducted in-depth research on the causes of malignant tumors, and the mechanism of gene carcinogenesis has slowly become clear. The so-called molecular targeted therapy is to design the corresponding therapeutic drugs at the cellular molecular level, targeting the defined oncogenic sites (the site can be a protein molecule or a gene fragment inside the tumor cell). Therefore, molecular targeted therapy is also called “biological missile”. Among the factors in the development of breast cancer, an oncogene called HER2 plays a major role. Nearly one-third of breast cancer patients have overexpression of HER2 gene, and the amplification of this gene has now become an important indicator in clinical medicine to assess the malignancy of breast cancer and the risk of recurrence and prognosis of breast cancer patients after surgery. Usually, the treatment of breast cancer is a combination of surgery, chemotherapy, endocrine therapy and radiation therapy. After a long period of medical practice, the above four treatments have achieved stable and reliable efficacy, but with the passage of time, they have encountered bottlenecks in their development as traditional treatments, and it is difficult to further improve the efficacy and have obvious toxic side effects, which can no longer meet the increasingly high As mentioned earlier, nearly one-third of the patients with breast cancer have been treated with the same treatment. As mentioned earlier, nearly one-third of breast cancer patients have overexpression of the oncogenic HER2 gene, and these patients have highly malignant tumor cells that are prone to recurrence and distant metastasis, making treatment more difficult and the future prognosis poor. In response to such characteristics, experts engaged in clinical drug research and clinicians worked closely together for many years to develop the first targeted therapy drug targeting HER2 gene, trastuzumab (trade name: Herceptin), which has been officially started to be used in the clinic for exactly 10 years since 1998 and has been proven to be an effective drug. Trastuzumab is a humanized antibody that specifically binds to the protein receptor expressed by gene HER2 outside the tumor cell membrane, thus blocking the information transmission channel of tumor cells for the purpose of treating malignant tumors. Clinical experience over the years has confirmed that the clinical efficiency of trastuzumab for HER2-positive breast cancer patients can reach 50%, which is much more effective than traditional chemotherapy, while effectively avoiding the cytotoxic side effects of chemotherapy, significantly improving the survival rate of breast cancer patients and reducing the risk of recurrence and metastasis. Since molecular targeted therapy has such amazing efficacy, can it be used by all breast cancer patients? Of course not, there are strict conditions for the use of molecular targeted therapy, it is targeted at a specific target, just like a missile needs radar and satellite to help find and lock on the target before it is launched, it also needs some auxiliary means. Take trastuzumab, before using it, we must first determine whether there is a target that can be attacked in breast cancer patients, that is, the protein receptor expressed by HER2 gene. Clinically, detecting HER2 gene is equivalent to using radar and satellite to locate the target, once the existence of the target is clear, using trastuzumab can achieve obvious striking effect; otherwise, if the target is not clear, that is to say, patients with negative response to HER2 gene patients with negative response, blind use will only result in half the effort. Therefore, HER2 gene expression should be routinely detected during the pre-surgical treatment of breast cancer patients, so as to create strong conditions for future molecularly targeted therapy and to achieve “precise guidance, bullet-free”. (Note: The trade name of the drug can be deleted to avoid suspicion.)