OBJECTIVES: I. Determine the objective response rate of women with HER2-neu overexpressing recurrent or metastatic breast cancer treated with trastuzumab (Herceptin) in combination with docetaxel. II. Determine the toxicity of this treatment regimen in these patients. III. Determine the duration of response to this treatment regimen in these patients. IV. Determine the time to progression in these patients after receiving this treatment regimen. V. Compare HER2-neu overexpression as determined by fluorescent in situ hybridization (FISH) versus immunohistochemistry, and correlate these findings with response to this treatment regimen in these patients. VI. Correlate HER2-neu activation by immunohistochemistry and the extracellular domain of HER2-neu by ELISA with response to this treatment regimen in these patients.