Inclusion Criteria:

1. Female patients with histologically or cytologically confirmed breast cancer.
2. The patients who have received prior chemotherapy including anthracycline and taxane.
3. Patients aged 20 - 74 years when giving informed consent.
4. Patients with an Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0 to 2.
5. Patients with a measurable lesion.
6. Patients having adequate function of major organs (bone marrow, liver, kidney and lungs).
7. Patients who have no carryover of efficacy or no adverse drug reactions from previous therapy that may affect the safety evaluation of the study drug.
8. Patients who have given written voluntary consent for participation in this study.
9. Patients with an expected survival of ≥ 3 months from the start of study drug therapy.

Exclusion Criteria:

1. Patients with systemic infection with a fever (≥38.0°C).
2. Patients with pleural effusion, ascites or pericardial fluid requiring drainage.
3. Patients with brain metastasis presenting clinical symptoms.

4. Patients with serious complications:

   • (1) Patients with uncontrollable cardiac disease such as ischemic heart disease and arrhythmia at a level of severity that needs to be treated (excluding left ventricular hypertrophy, mild left ventricular volume overload and mild right leg block that accompany hypertension)
   • (2) Patients with myocardial infarction within 6 months prior to study entry
   • (3) Patients with a complication of hepatic cirrhosis
   • (4) Patients with interstitial pneumonia and pulmonary fibrosis
   • (5) Patients with a bleeding tendency
5. Patients with an active double cancer.
6. Pregnant women or nursing mothers.
7. Patients who have received extensive radiotherapy (≥30% of bone marrow).
8. Patients who refuse to receive the supportive therapy of blood transfusion for myelosuppression.
9. Patients who are participating in other clinical studies.
10. Patients who are judged inappropriate for this study by the investigator or subinvestigator.