Inclusion Criteria (major highlights):

• Patient is an adult female with histologically or cytologically confirmed carcinoma of the breast for whom single-agent cytotoxic chemotherapy is indicated
• Patient can have either measurable or non-measurable disease by RECIST.
• Patient has received prior therapy (administered in the neoadjuvant, adjuvant and/or metastatic setting) with an anthracycline, a taxane and capecitabine
• Patient has minimum of 2 and a maximum of 5 prior cytotoxic chemotherapy regimens with the last dose administered within 6 months. A minimum of two chemotherapy regimens had to be for locally recurrent and/or metastatic disease. All therapy received prior to a diagnosis of metastatic disease (eg, neoadjuvant, adjuvant or repeated adjuvant therapy following a second resection) is counted as one regimen.
• Patient has Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.
• Adequate hematopoietic, liver and kidney functions.

Exclusion Criteria (major highlights):

• Patient with chemotherapy within 21 days, radiotherapy within 14 days, biological therapy with 14 days, hormonal therapy within 7 days and investigational therapy within 21 days prior to randomization.
• Patient with any major surgery within 28 days prior to randomization.
• Patient with concurrent use of biologic agents for the treatment of cancer including antibodies or any investigational agent(s).
• Patient with prior treatment for cancer with a camptothecin derivative.
• Patient with chronic or acute GI disorders resulting in diarrhea of any severity grade; patients who are using chronic anti-diarrheal supportive care to control diarrhea in the 28 days prior to randomization.
• Patient received pharmacotherapy for hepatitis B or C, tuberculosis or HIV.
• Patient with known cirrhosis diagnosed with Child-PUGH Class A or higher liver disease.
• Patient with prior malignancy (other than breast cancer) except for non-melanoma skin cancer and carcinoma in situ (of the cervix or bladder), unless diagnosed and definitively treated more than 5 years prior to randomization.
• Patient requiring daily use of oxygen supplementation in the 28 days prior to randomization.
• Patients with significant cardiovascular impairment.