Breast cancer is the most common malignant tumor in women, and its incidence has been increasing year by year in recent years. Surgery is an important means of breast cancer treatment, and the rational application of postoperative adjuvant chemotherapy, endocrine therapy and preoperative neoadjuvant therapy has significantly improved the treatment effect of operable breast cancer patients. However, a considerable number of patients still have recurrence or are resistant to conventional treatment. With the development of molecular biology technology, tumor molecular targeting drugs have gradually become a hot spot in tumor treatment. At present, some molecular targeted drugs have been successfully applied in clinical or entered clinical trials in the field of breast cancer treatment. 1.Trastuzumab Trastuzumab is a humanized monoclonal antibody, which is the first molecularly targeted therapeutic drug used in the clinic, mainly for the treatment of epidermal growth factor receptor 2 (HER2)-positive breast cancer, and its mechanism of action is to inhibit the activation of signaling system by blocking HER2 receptor dimerization after binding to the extracellular region of HER2 receptor, thus inhibiting the proliferation of tumor cells; meanwhile, the trastuzumab induces antibody-mediated cytotoxic effects in tumor cells in vivo. Four recently reported large-scale, multicenter, randomized clinical studies showed that trastuzumab significantly reduced the risk of recurrence and prolonged the survival of patients with different subtypes of HER2-positive patients in early-stage breast cancer. Therefore, trastuzumab has become part of the standard adjuvant therapy for early-stage HER2-positive breast cancer. Trastuzumab has synergistic effects with platinum, doxorubicin, and vincristine, and stacking effects with adriamycin, paclitaxel, and cyclophosphamide. The combination chemotherapy regimens containing trastuzumab are: anthracycline sequential paclitaxel combined with trastuzumab regimen, trastuzumab alone after standard chemotherapy, and doxorubicin and carboplatin combined with trastuzumab. For patients with HER2-positive locally advanced breast cancer receiving preoperative neoadjuvant chemotherapy, the combination of trastuzumab may also be considered to be able to improve the pathological complete remission rate (pCR). In addition, trastuzumab monotherapy in first line may provide the greatest survival benefit for patients with HER2-positive recurrent metastatic breast cancer. The recommended dose of trastuzumab as a single agent or in combination with chemotherapy is generally an initial dose of 4 mg/kg administered intravenously over 90 minutes, followed by a weekly maintenance dose of 2 mg/kg for a standard course of 1 year. The main adverse effect of trastuzumab is cardiotoxicity, but the severity is mild and easily reversible. Clinically, it should not be used concomitantly with anthracyclines. Echocardiographic assessment of left ventricular ejection fraction should be performed prior to dosing and cardiac function should be monitored every 3 months during dosing. Other adverse reactions include fever, chills, abdominal pain, weakness, chest pain, headache, diarrhea, and vomiting. Although trastuzumab is more expensive to treat, it also has better therapeutic benefits. Therefore, trastuzumab treatment group is considered to have better cost-effectiveness compared with the observation group. 2. Lapatinib Lapatinib is an oral, reversible tyrosine kinase inhibitor that inhibits tyrosine phosphorylation of both the epidermal growth factor receptor (EGFR, HER1) and HER2 in tumor cells, with significantly better efficacy than drugs that inhibit only one of these targets. This drug is the second molecularly targeted drug approved for marketing in breast cancer after trastuzumab, mainly for the treatment of advanced breast cancer. The existence of the blood-brain barrier makes it difficult for commonly used chemotherapeutic agents and molecularly targeted therapeutic agents such as trastuzumab to enter, and the extremely low intracranial blood concentration provides a “refuge” for tumor cells. Lapatinib is a small molecule that can cross the blood-brain barrier and can therefore be used to treat brain metastases from breast cancer. Lapatinib is not cross-resistant to trastuzumab and may still be effective in trastuzumab-resistant breast cancer. Lapatinib and capecitabine are used in combination in patients with progressive, HER2-positive breast cancer who have used anthracyclines, paclitaxel, and trastuzumab. It is administered orally at 250 mg per day for the first 14 days of the recommended 21-day course, in combination with daily capecitabine. The drug is well tolerated, with the main adverse effects being diarrhea and skin rash. Reversible cardiac damage has been reported in a small number of patients. Bevacizumab The concept of “tumor growth dependent on angiogenesis” was first introduced by Folkman in 1971. Bevacizumab is a recombinant humanized monoclonal antibody that inhibits tumor growth by competitively binding to the VEGF receptor and blocking VEGF-mediated biological activity, thereby inhibiting endothelial cell mitosis and reducing tumor neovascularization. It is the first drug approved for marketing to inhibit tumor angiogenesis. As an angiogenesis inhibitor, bevacizumab itself has no direct effect on killing tumor, but only indirectly kills tumor by destroying tumor blood vessel formation, therefore, bevacizumab is mostly used in combination with chemotherapy drugs paclitaxel and capecitabine for breast cancer treatment in clinical practice. Bevacizumab is usually given as an intravenous infusion once every 2 or 3 weeks until the disease progresses. The most common adverse reactions are: rash, diarrhea, hypertension, thrombosis, and proteinuria. Targeted drug therapy for breast cancer is a very big breakthrough. It has changed the paradigm and mechanism of traditional treatment, so it is more specialized. But it needs to be emphasized: the breakthrough is not a substitute at the same time. Do not think that with molecular targeted drugs, traditional chemotherapy is useless and not needed. The best treatment strategy is that the advantages of new drugs should be used on top of standard conventional treatment. Many targeted drugs need to be used in combination with chemotherapy, that is, to kill some tumor cells by chemotherapy first, and then inhibit them with targeted drugs.