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.

Inclusion Criteria:

1. Female patients with histologically or cytologically confirmed breast cancer.
2. Patients with inoperable or recurrent metastatic breast cancer regardless of the metastatic site and number, excluding symptomatic central nervous system metastases.
3. Patients with HER2-negative disease confirmed as ISH negative or IHC 0, 1+ or 2+ (Those with IHC 2+ are eligible, if the additional ISH test results are negative. Those are ineligible who are with any positive results of estrogen receptor or progesterone receptor test on primary and recurrent lesion).
4. Patients who are resistant to hormone therapy.
5. Patients with indication for the first or second line chemotherapy in HER2-negative hormone-resistant inoperable or recurrent metastatic breast cancer who are scheduled to receive the chemotherapy.
6. Patients with the Eastern Cooperative Oncology Group (ECOG) performance status score 0-3 at the time of enrollment.
7. Patients with adequate bone marrow and major organ function judged by the primary physician.
8. Patients who have signed written informed consent to participate in this study.

Exclusion Criteria:

1. Patients with symptomatic metastasis in the central nervous system.
2. Patients with a previous history of hypersensitivity to any component of drugs which will be administered in the treatment.
3. Patients who are considered to be inappropriate for the study participation by the primary physician.

Female patients with HER2-negative hormone-resistant inoperable or recurrent metastatic breast cancer, who are scheduled to receive the first or second line chemotherapy in clinical practice in Japan.