The purpose of this phase II, randomized, open-label clinical trial is to study 2 schedules of single-agent Irinotecan in women with metastatic breast cancer who have experienced failure of prior therapy with an anthracycline, a taxane, and capecitabine. Patients will receive Irinotecan capsules either once each day for 5 days, or once a day for 14 days in 3 week cycles.

Inclusion Criteria:

• Women with diagnosis of primary adenocarcinoma of the breast
• Presence of locally advanced or metastatic disease non-amenable to surgery or radiation therapy with curative intent
• At least one measurable lesion >20mm (or >10 mm with spiral CT scan)
• Must have received (and failed) prior treatment with an anthracycline, a taxane, and capecitabine in the adjuvant and/or advanced disease treatment setting
• Women at least 18 years old, with performance status 0-2

Exclusion Criteria:

• Prior treatment with another topoisomerase I inhibitor
• Current enrollment in another clinical trial