This phase 11 study was designed to evaluate the safety and efficacy of weekly docetaxel (36 mg/m(2)) for the treatment of metastatic breast cancer in 47 frail and/or elderly patients who were ineligible for the standard 3-weekly docetaxel (100 mg/m(2)) regimen. Reasons for ineligibility to the latter were age greater than or equal to 70 years (10 patients), poor hematological reserves (15 patients), impaired liver function (eight patients), intolerance to previous taxanes administered 3-weekly without demonstrated resistance (five patients) or any combination of these reasons (nine patients). There was a median of two prior chemotherapy regimens and more than 60% had a WHO performance score at baseline of 2-3. A total of 408 weekly administrations were given over a period of 525 weeks (78% of the intended dose intensity) and the median cumulative dose of docetaxel per patient was 278 mg/m(2). The incidence of serious adverse events was low. Grade 3 neutropenia occurred in six patients and grade 4 in four patients. Of these 10 patients, eight had pre-existing hematological abnormalities and four developed neutropenic fever. Neurotoxicity was mild and grade 3 paraesthesia occurred in one patient The overall objective response rate in 37 evaluable patients was 30% and responses were observed in all subgroups of patients. We conclude that weekly docetaxel (36 mg/m(2)) is active, safe and well tolerated in heavily pre-treated frail/elderly patients with poor prognostic features, including low performance scores and multiple metastatic sites, who would not be eligible for treatment with the standard 3-weekly regimen. (C) 2004 Lippincott Williams Wilkins.