A Study to Evaluate Inetetamab + Pyrotinib + Chemotherapy in Previously Untreated HER2-Positive Metastatic Breast Cancer

Inclusion Criteria:

1. Aged 18 \~ 75 years old, female;
2. Patients with HER2-positive breast cancer defined as immunohistochemical (IHC) test + + +, or FISH test positive;
3. According to the Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1, at least one measurable lesion exists;
4. ECOG PS score 0-1 points;
5. No systemic antitumor therapy (except first line endocrine therapy) in relapse/metastasis;
6. If prior anti-HER2 therapy (including trastuzumab, trastuzumab biosimilar, Inetetamab, pertuzumab, tyrosine kinase inhibitors such as pyrotinib, T-DM1) was used in the (neo) adjuvant phase, the interval between the end of anti-HER2 therapy to the diagnosis of relapse/metastasis was ≥ 12 months;
7. Adequate organ function;
8. Expected survival ≥ 3 months;
9. Patients voluntarily sign informed consent, have good compliance and are willing to cooperate in follow-up.

Exclusion Criteria:

1. Known to have a history of hypersensitivity to the drug components of this protocol;
2. Investigators judged that they were not suitable for systemic chemotherapy;
3. Endocrine therapy drugs were used within 14 days before baseline;
4. Active brain metastases;
5. Only bone or skin as target lesions;
6. Patients with other malignant tumors within 5 years, excluding cured cervical carcinoma in situ, cutaneous basal cell carcinoma or squamous cell carcinoma;
7. Grade≥3 peripheral neuropathy according to CTCAE 5.0 criteria;
8. Patients who have previously received more than the following cumulative doses of anthracyclines: doxorubicin or liposomal doxorubicin \> 360 mg/m2, epirubicin \> 720 mg/m2, mitoxantrone \> 120 mg/m2, others (such as other anthracyclines or multiple anthracyclines, cumulative dose \> 360 mg/m2 of doxorubicin);
9. Received major surgical procedures or significant trauma within 4 weeks before randomization, or patients are expected to receive major surgical treatment;
10. Serious heart problems or discomfort;
11. Dysphagia, chronic diarrhea, intestinal obstruction and other factors affecting administration and absorption;
12. History of immunodeficiency, including HIV infection, or suffering from other acquired, congenital immunodeficiency diseases, or history of organ transplantation; 13. Participated in other drug clinical studies within 4 weeks before screening;

14\. Presence of third space effusion (such as pleural effusion and ascites) that cannot be controlled by drainage or other methods; 15. Pregnant or lactating female patients, women of childbearing age who cannot take effective contraceptive measures throughout the trial; 16. With severe concomitant diseases or interfere with the planned treatment or any other condition that is not suitable for participating in this study, such as active hepatitis B, lung infection requiring treatment.