Breast cancer patients require targeted therapy when they present with positive gene expression in molecular biology tests, most often for the HER-2 gene, a member of the transmembrane tyrosine kinase growth factor receptor family. Current studies have shown that about 20-30% of breast cancer patients have amplification or overexpression of HER-2 gene. This group of patients is prone to recurrence and metastasis because of rapid tumor progression, and has a poor prognosis, so they need to be treated with drugs that target this gene expression positivity. Currently, the most commonly used drug for patients with positive HER-2 gene expression is Herceptin. Herceptin can reduce the risk of recurrence by about 50% and the risk of death by about 30%, so the use of Herceptin in adjuvant therapy has increased the chance of obtaining a cure for patients with early-stage breast cancer and has since changed the traditional treatment paradigm of breast cancer drugs. HER-2 gene status testing is required for all newly diagnosed invasive breast cancer patients. Proper monitoring and evaluation of HER-2 protein expression and gene amplification status in breast cancer is crucial for clinical treatment and prognosis of breast cancer.