PRIOR CONCURRENT THERAPY: Biologic therapy: No prior bone marrow transplantation or autologous stem cell infusion following high-dose adjuvant chemotherapy for metastatic disease No concurrent immunotherapy (including humanized anti-HER2 antibody) Chemotherapy: See Disease Characteristics See Biologic therapy No prior chemotherapy for metastatic breast cancer No prior gemcitabine or taxane No other concurrent chemotherapy Endocrine therapy: See Disease Characteristics Prior antitumoral hormonal therapy allowed No concurrent hormonal therapy excluding contraceptives and replacement steroids Radiotherapy: See Disease Characteristics At least 2 weeks since prior radiotherapy and recovered No concurrent radiotherapy Surgery: See Disease Characteristics Other: Recovered from prior therapy At least 30 days since prior investigational drugs No concurrent investigational drugs Concurrent bisphosphonate therapy allowed if not begun or stopped within 4 weeks before study