Maintenance Bevacizumab or Observation After Taxane Based First Line Chemotherapy In Metastatic Breast Cancer

Inclusion Criteria: * Written informed consent * Age ≥18 years * Patients with histologically or cytologically confirmed, HER2-negative, metastatic Breast Cancer * No prior first line treatment for metastatic Breast Cancer * Previous hormonotherapy for metastatic Breast Cancer is allowed * One or more measurable lesions (≥1cm in diameter with spiral CT scan or ≥2cm with conventional techniques) according to RECIST criteria * ECOG performance status ≤2 * Adequate haematological, renal and hepatic function * Urine protein \<2+ (dipstick) * Life expectancy of ≥12 weeks Exclusion Criteria: * Previous first line treatment for metastatic colorectal cancer(progression \>12 months after the end of adjuvant treatment) * Previous radiotherapy to target lesions * Patients with brain metastases and/or cancerous meningitis * Presence or history of other neoplasm except properly treated basal cell skin cancer or in situ cervical carcinoma * Patients participating in interventional clinical trial