In this first reported study of weekly paclitaxel administered as first-line chemotherapy for metastatic breast cancer, paclitaxel 100 mg/m2 was administered in a 1-h infusion on a weekly basis to 35 patients who may previously have received adjuvant chemotherapy (but not taxane-containing regimens), but not for advanced or metastatic disease. A median of 14 infusions per patient was given at a mean delivered dose intensity of 94 mg/m2 per week. In 33 assessable patients, a complete response (CR) was observed in 1 patient and partial responses (PRs) in 12 patients, producing an overall response rate of 40%. Stable disease (SD) was observed in 17 patients, of whom 9 were stabilized for more than 24 weeks. Thus, clinical benefit (CR+PR+SD(> or = 24 weeks)) was observed in 67% of the patients. Time to progression was 189 days, the duration of response 180 days and overall survival 544 days. Five patients developed grade 3 neutropenia and five patients grade 3 neurotoxicity. Thus, this study has shown that weekly paclitaxel as first-line therapy for metastatic or advanced breast cancer produces comparable response rates and less toxicity than when the drug is given every three weeks.