Combination of Oral WX-671 Plus Capecitabine vs. Capecitabine Monotherapy in First-line Her2-negative Metastatic Breast Cancer

Inclusion Criteria: * Females aged ≥ 18 years * Patients appropriate for palliative first-line, mono chemotherapy with capecitabine * Histological or cytological confirmed, non-inflammatory metastatic breast cancer * Availability of paraffin-embedded tumor tissue from the primary resection or biopsy of a metastatic lesion. * HER2-negative breast cancer * Complete staging within 2 weeks prior to randomization (4 weeks for bone scan). * Radiologically confirmed disease * ECOG performance status of ≤ 2 * Ability to understand and willingness to voluntarily sign and date a written informed consent form before screening * Negative pregnancy test (urine or serum) within 3 days before first study drug for women of childbearing potential. Use of effective contraception during the study and for 3 months after stopping study drug treatment. * Normal organ and marrow function as defined by laboratory parameters (obtained within the screening period) within the following limits: * neutrophils \>= 1.5 x 109/L; * platelets \>= 100 x 109/L; * hemoglobin \>= 9.0 g/dL (5.6 mmol/L). * total bilirubin \<= 1.5 x upper limit of normal (ULN); * aspartate aminotransferase (AST)/ALT \<= 2.5 x ULN (\< 5.0 x ULN for patients with liver metastases); * serum creatinine \<= 2 x ULN, or calculated creatinine clearance \>45 mL/min according to Cockroft and Gault formula). Exclusion Criteria: * Endocrine therapy completed within 2 weeks before the start of treatment (i.e. previous hormone therapy is allowed provided that there is a washout period of 2 weeks). * Prior chemotherapy or biologic therapy for metastatic disease. * Major surgery within 4 weeks prior to the start of treatment. * Other anti-cancer treatment (e.g. hormones) within 2 weeks before the start of treatment. * Treatment within 12 months with adjuvant 5-FU containing chemotherapy (regarded as indicating 5-FU resistance) and/or prior capecitabine therapy. * Radiation therapy. Palliative radiation of stable, non-target lesions more than 2 weeks before the start of treatment is allowed, provided patients have recovered from the radiation side-effects. * History of or radiological evidence of brain metastasis including previously treated, resected or asymptomatic brain lesions or leptomeningeal involvement. * Active seizure disorder or history of cerebrovascular accident (CVA) or transient ischemic (TI) attack within the past 12 months. * History of other malignancy within the last 3 years except for surgically cured non-melanoma skin cancer or cervical carcinoma in situ. * Active cardiac disease e.g. unstable angina, congestive heart failure, myocardial infarction (MI) within the preceding 6 months. * Any medical condition prohibiting standard imaging procedures * Pregnant or breast-feeding. * Any unrelated illness, e.g. active infection requiring parenteral antibiotics, inflammation, medical condition or laboratory abnormalities, which in the judgment of the investigator might significantly affect patients' study participation. * Any surgical or medical condition that might significantly alter the absorption, distribution, metabolism or excretion of either study drug. * Known hepatitis B/C or HIV (human immunodeficiency virus) infection.