Patient description: The patient is a 42 year-old postmenopausal woman who had a screening sonogram which revealed an abnormality in the right breast. She had no palpable masses on breast exam. Core biopsy was done and revealed a 1.8 cm infiltrating ductal breast carcinoma in the left upper outer quadrant. Lumpectomy was done and the surgical margins were clear. The tumor was HER2-positive and ER/PR negative. Axillary sampling revealed 1 positive lymph node out of 12 sampled. CXR was unremarkable. She is using “well women” multivitamins daily and no other medication. She smokes frequently and consumes alcohol occasionally. She is in a relation with only one partner and has a history of 3 pregnancies and live births. She breastfed all three children.

Clinical trial eligibility criteria: eligible ages (years): 18.0-75.0,  Metastatic Breast Cancer Adult female patients with advanced breast cancer diagnosed by pathology (aged 18-75, including 18 and 75 years old), not suitable for surgical resection or radiation therapy for the purpose of cure Pathological examination confirmed ER and / or PR positive, HER-2 negative (Positive ER expression: immunohistochemistry >1% tumor cell staining; Positive PR expression: immunohistochemistry >1% tumor cell staining; HER-2 negative: immunohistochemistry is 0,1+, or FISH/CISH negative when immunohistochemistry is 2+) Patients with advanced breast cancer who have no disease progression after a 4-8-course first-line chemotherapy regimen (the effect is evaluated as complete response/ partial response/ stable disease). Capecitabine monotherapy as first-line chemotherapy is allowed and the courses of treatment should be limited to 6 WHO physical status 0-1 points, estimated lifetime at least 3 months Imaging examinations within 3 weeks before enrollment were required for assessing tumor lesions before maintenance treatment (Examination results from local Tertiary A hospital are available) Previous treatment-related toxicity should be relieved to ≤ Grade 1 according to NCI CTCAE (version 4.03) before randomization (Except for hair loss and other toxicities that are not at risk to the patient's safety based on the investigator's judgment) The routine blood test was normal within 1 week before enrollment: WBC ≥3.0×10^9／L, b. ANC ≥1.5×10^9／L, c. PLT ≥100×10^9／L The liver and kidney function test was normal within 1 week before enrollment (Take the normal value of the laboratory of each research center as the standard): a. TBIL≤1.5× Upper Limit of Normal (ULN)b. ALT/AST≤2.5×ULN（Liver metastasis patients ≤5xULN） c. Serum Cr ≤1.5×ULN, or Ccr ≥60 ml/min Informed consent form signed before enrollment  Cannot be grouped if any of the following is true Newly developed central nervous system metastasis or symptom control of central nervous system is less than 4 weeks. (Patients with asymptomatic brian metastases which was stable more than 4 weeks by imaging assessment and do not need corticosteroid therapy are allowed to enrollment) Diagnosis of any other malignant tumor within 3 years before randomization, except for adequately treated basal cells or squamous cell skin cancer or cervical cancer in situ Endocrine therapy for advanced disease Pregnant or breast-feeding patients Patients with accompanying disease or situation that may interfere with the study, or any serious medical problems that may affect the safety of the subject (for example, uncontrolled heart disease or high blood pressure, active or uncontrolled infection, active hepatitis B virus infection) Patients who were unable to tolerate capecitabine toxicity were first identified in first-line treatment Patients with recurrent metastatic disease within 2 years of adjuvant endocrine therapy (including 2 years)