A ReaL World Study of DS-8201

Inclusion Criteria: 1. Male or female aged 18 or above; 2. The Eastern Cooperative Oncology Group (ECOG) physical condition score of the United States is ≤2; 3. HER2 positive (IHC 3+ or IHC 2+ and ISH+) confirmed by tumor histology or cytology, and having received one or more anti-HER2 drug treatments previously; Or low expression of HER2 confirmed by tumor histology or cytology (IHC 1+ or IHC 2+ and ISH-), and having received at least one systemic treatment in the metastatic disease stage previously, or unresectable or metastatic breast cancer that relapsed during adjuvant chemotherapy or within 6 months after the completion of adjuvant chemotherapy; 4. Receive goldtrastuzumab treatment in the advanced stage; 5. During the study period, voluntarily abide by this trial protocol and receive regular follow-ups; 6. All women of childbearing age, fertile men or their spouses who have no plans for fertility or sperm donation throughout the trial period until 6 months after the last dose, or who voluntarily take effective contraceptive measures. Exclusion Criteria: 1. Pregnant or lactating women; 2. Those with acute or chronic infections, or those with other serious diseases at the same time, are judged by the researchers as unsuitable for this study; 3. Having suffered from other malignant tumors within 5 years (excluding the following situations: cured basal cell carcinoma of the skin, carcinoma in situ of the cervix, and papillary thyroid carcinoma; A second primary cancer that has been completely cured and has no recurrence within five years; Researchers have clearly identified which primary tumor source the metastatic foci belong to. 4. Those with mental illness or mental disorders, poor compliance and inability to cooperate and describe treatment responses; 5. Those with severe organic diseases or major organ failure, such as decompensated heart, lung, liver or kidney failure, which makes them unable to tolerate treatment; 6. Patients allergic to trastuzumab; 7. Patients who changed their treatment regimens after trastuzumab treatment due to reasons other than disease progression or intolerable adverse reactions; 8. The researcher believes that the patient has other circumstances that make them unsuitable for participating in this study