OBJECTIVES: I. Assess the antitumor activity and toxicity of two different schedules of irinotecan in the treatment of patients with refractory metastatic breast cancer who have received 1 or 2 previous chemotherapy regimens (up to one prior therapy for metastatic disease and one for adjuvant therapy). II. Compare the time to progression, survival, and quality of life of these patients on these 2 different schedules of irinotecan.