Eribulin Treatment as 1st-line or 2nd-line Chemotherapy for HER2-negative Hormone-resistant Inoperable or Recurrent Metastatic Breast Cancer

This is a observational study in a real-world setting, not requiring determining a dosage regimen, dose reduction criteria, rest period criteria and withdrawal criteria. The purpose of the study is to investigate the efficacy of eribulin as the first or second line chemotherapy to prolong overall survival and to explore factors affecting the survival in patients with HER2-negative hormone-resistant inoperable or recurrent metastatic breast cancer who scheduled to receive the first or second line chemotherapy in clinical practice in Japan. The total duration of the study will be a maximum of 5 years, consisting of 2-year enrollment period and 3-year observational period; the duration of patient participation will be 3 years. All patients will receive adequate treatment for breast cancer which selected by the primary physician after enrollment using the Japanese Breast Cancer Society Clinical Practice Guideline of Breast Cancer and the National Comprehensive Cancer Network (NCCN) Clinical Practice Guidelines in Oncology. Investigators at the investigational sites will enter patient data into an electronic data capture (EDC) system up to the third chemotherapy in the study. The end of the study is defined as the time the last patient completes observational period. Patients will primarily be assessed by overall survival (OS) of the first line chemotherapy.