Compare Apatinib Plus Capecitabine Versus Capecitabine in Maintenance Therapy for Patients With Advanced Triple-negative Breast Cancer

Inclusion Criteria: 1. Age：18\~75 years; 2. Triple-negative breast cancer (TNBC) confirmed by histology examination; 3. patients had received first-line combination chemotherapy for advanced metastatic disease, and had a complete response, partial response or stable disease according to Response Evaluation Criteria In Solid Tumors (RECIST) 1.1 criteria; 4. received endocrine therapy for metastatic disease before first-line chemotherapy were allowed; 5. Eastern Cooperative Oncology Group (ECOG) performance status of 0-1; 6. A life expectancy of more than 12 weeks; 7. Baseline blood routine examination in accordance with the following criteria : ANC≥1.5×109/L，PLT≥90×109/L，Hb≥90g/L; 8. Liver and renal function in accordance with the following criteria: total bilirubin less than 1.5 times the upper limit of normal value; aspartate aminotransferase (AST), or alanine aminotransferase (ALT) less than 2.5 times the upper limit of normal value, less than 5 times the upper limit of normal value in patients with liver metastases. the creatinine clearance rate calculated greater than 60 mL/min; 9. Females of childbearing potential must be a pregnancy test in 7 days before participating ( including serum or urine), and the results were negative, and they are willing to take effective contraceptive methods During the trial and within 8 weeks after the last dose; 10. Obtain informed consent from patients before starting any research-related operations and treatments to confirm that patients are willing to participate in this study and comply with research-related requirements. Exclusion Criteria: 1. Metastasis/recurrence occurs within 6 months of adjuvant chemotherapy; 2. controlled high blood pressure, systolic blood pressure ≥150mmHg or diastolic blood pressure ≥100mmHg; 3. urine routine test with urinary protein more than ++, or 24 hour urinary protein more than 1.0 g; 4. abnormal coagulation function (INR \> 1.5 or prothrombin time (PT) \> ULN+4 seconds or APTT \>1.5 times the ULN); 5. Pregnant or lactating woman; 6. Symptomatic brain parenchymal and/or pia mater metastases without treatment and control; 7. Patients with Other malignant tumors in the past 5 years, except for fully treated cervical carcinoma in situ, cutaneous squamous cell carcinoma or well-controlled localized basal cell skin cancer; 8. Mental illness or other condition that affects patient compliance; 9. serious and uncontrollable systemic diseases (eg clinically significant cardiovascular disease, lung or metabolic disease, arteriovenous thrombosis, etc.) happened recently; 10. Can not take or absorb oral drugs; 11. Receiving any other testing drugs, or participating in other clinical trial 30 days before being enrolled in this trial; 12. The patient has previously received treatment with an anti-angiogenic drug (whether adjuvant or palliative); 13. Known or suspected to be allergic to any research drug or excipient; 14. Any other researcher believes that it is not appropriate to participate in this test.