As a malignant tumor that threatens women’s health, the incidence of breast cancer is on the rise in China, especially in large and medium-sized cities such as Shanghai and Beijing, where it is the most prevalent malignant tumor among women. With the publicity of media and the popularization of our daily health knowledge, many people have heard about some common treatments for breast cancer. For example, radical surgery, breast-conserving treatment, radiotherapy, chemotherapy and so on. However, with the advancement of technology, doctors are no longer armed with the above-mentioned conventional weapons, there is a new member in the arsenal of breast cancer treatment, “targeted therapy”. What is this treatment all about? Targeted therapy means that the target or object of treatment is precise, hitting the cancer cells precisely and affecting the normal cells of the body relatively little. Just like the demolition and targeted blasting of certain buildings we see in our lives, targeted drugs can act directly or indirectly on breast cancer cells so that the cells can no longer reproduce and survive, and ultimately serve to kill breast cancer cells. In recent years, with the advancement of molecular biology technology, people have studied more and more deeply the mechanism of tumor occurrence, development and invasion from the molecular level, and found that there are abnormalities of several signaling pathways in breast cancer. These signaling pathways can transmit some signals that favor tumor proliferation and metastasis to cancer cells, promoting tumor development and metastasis. For example, human epidermal growth factor receptor (HER) family, angiogenic pathway, cell proliferation pathway, cell cycle regulation, apoptosis pathway, etc. Encouraging results have been achieved with targeted therapies against these pathways. Trastuzumab, a monoclonal antibody against HER2, was the first molecularly targeted drug in the field of breast cancer treatment and has been used since 1998 for the treatment of postoperative recurrent or metastatic breast cancer. Currently, trastuzumab plays an extremely important role in the treatment of both early and advanced breast cancer. The target of this drug is HER2-positive breast cancer, and only with this target can our targeted drugs work. This is why human epidermal growth factor receptor (C-erbB2 or Her2) is routinely tested in the pathology of breast cancer patients after surgery. When the routine pathology test for C-erbB2 or Her2 is 3 plus (+++), we consider it to be Her2 positive. If it is 2 plus (++), it needs to be further confirmed by other methods. Since targeted drugs are specific to kill breast cancer cells, does it mean that there are no side effects? It should be said that targeted drugs have fewer side effects than traditional chemotherapy, but they are not free of side effects at all. Because targeted drugs target various signaling pathways that exist in normal cells but are not as active as cancer cells, targeted drugs also have their specific adverse effects. For example, trastuzumab requires attention to cardiotoxicity, especially in patients who have received anthracycline chemotherapy before, and need to pay attention to the regular review of the heart. Currently, only trastuzumab has been approved by the State Food and Drug Administration (SFDA), and many related targeted drugs are in the clinical research stage. For example, small molecule tyrosine kinase inhibitors, phosphatidylinositol-3-kinase (PI3K)/mammalian target of rapamycin (mTOR) inhibitors and heat shock protein 90 (hsp90) antagonist therapy as well as treatment targeting insulin-like growth factor-1 receptor (IGF-1R), etc. There are many relevant clinical trials being conducted worldwide, including the Peking University People’s Hospital Breast Center, and we are also currently conducting a clinical trial of a small molecule tyrosine kinase inhibitor. So patients who have failed after trastuzumab treatment can consider participating in these clinical trials for better results.