This international study will study how metastatic breast cancer responds to the investigational drug treatment, what are the side effects of the investigational drug when given to women with metastatic breast cancer and how often do these side effects occur. The study will also analyze how fast investigational drug and its breakdown products are cleared from the blood in these patients.

Inclusion Criteria:

• Locally advanced or metastatic breast cancer not amenable to surgery or radiation with curative intent
• Must have received any chemotherapy regimen in the past
• Evidence of tumor resistance to last chemotherapy defined as progression after 6 months of previous chemotherapy for advanced disease
• Must have measurable (by imaging techniques) disease
• Adequate bone marrow, liver and renal function
• Must provide evidence of informed consent and willingness and ability to comply with scheduled visits, treatment plan and study procedures.

Exclusion Criteria:

• Received more than 2 prior chemotherapy regimens for metastatic disease
• Received in the past another drug of the same class as the investigational drug, i.e. topoisomerase I inhibitor
• Enrolled in another clinical intervention study
• Pregnancy, breast feeding, fertile women refusing to use reliable contraceptive methods
• Cardiac or thrombotic event in the last 12 months
• Brain metastases