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.