Herceptin is a class of humanized monoclonal antibodies that can treat malignancies with high expression of HER2 (also known as C-erB-2, hereafter commonly referred to as HER2) and is currently used for patients with Her2-positive breast and gastric cancers. What is HER2 positivity in the first place? The following basic conditions must be met: HER2 immunohistochemistry (IHC) ++ (must be three +) or IHC of ++ (two +), at which point further FISH (detection of gene amplification) testing must be performed and positive. For metastatic lesions, try to re-puncture the biopsy to detect HER2 expression status instead of taking it for granted that the metastatic lesion is the same as the primary lesion based on the primary lesion. Secondly, for HER2-positive breast cancer, postoperative adjuvant chemotherapy, except for stage Ia, should be routinely treated with Herceptin for at least six months, preferably no longer than one year, unless there is severe allergic reaction or cardiotoxicity, it should be continued after the cessation of chemotherapy until the end of the course, which can be combined with endocrine therapy drugs such as triamcinolone or letrozole. In patients with metastatic breast cancer (note that metastatic lesions must be biopsied and re-evaluated for HER2 status) this drug can be used in combination with chemotherapeutic agents to significantly prolong survival, depending on efficacy and tolerability, and can be used for as long as the lesions do not progress and are tolerated (provided that funding is acceptable). Finally, about 1/4 to 1/5 of patients with gastric cancer are HER2-positive. For those patients with recurrent or metastatic gastric cancer, HER2 expression status can be tested and those who are positive can be treated with Herceptin in combination, which is currently not advocated for postoperative adjuvant therapy.