OBJECTIVES: I. Assess the toxicity and efficacy of nitrocamptothecin in patients with locally recurrent or metastatic breast cancer. II. Determine the duration of response and time to treatment failure in these patients with this treatment regimen. III. Correlate serum levels of nitrocamptothecin and its lactone metabolite with response and toxicity in these patients. IV. Correlate topoisomerase I and II levels with toxicity and response in these patients.