RATIONALE: Drugs used in chemotherapy, such as gemcitabine hydrochloride and genistein, work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. Giving gemcitabine hydrochloride together with genistein may kill more tumor cells.

PURPOSE: This phase II trial is studying how well giving gemcitabine hydrochloride together with genistein works in treating women with stage IV breast cancer.

OBJECTIVES:

Primary

• Determine the objective response rate in patients with stage IV breast cancer treated with gemcitabine hydrochloride and genistein.

Secondary

• Determine the duration of response and survival of patients treated with this regimen.
• Determine the time to disease progression in patients treated with this regimen.
• Determine the quantitative and qualitative toxic effects of this regimen in these patients.
• Correlate plasma genistein levels with response in patients treated with this regimen.

OUTLINE: Patients receive oral genistein once daily on days -7 to 1. Patients also receive gemcitabine hydrochloride IV on days 1 and 8 and oral genistein once daily on days 1-21. Courses repeat every 21 days in the absence of disease progression or unacceptable toxicity.

PROJECTED ACCRUAL: A total of 36 patients will be accrued for this study.

DISEASE CHARACTERISTICS:

• Histologically or cytologically confirmed breast cancer

  • Stage IV disease
  • Clinical and/or radiological evidence of metastatic disease

• Measurable disease

  • Prior radiotherapy allowed provided there is ≥ 1 measurable disease site outside the radiation field

• No active CNS metastases

  • Previously treated CNS metastases allowed provided disease is stable for ≥ 3 months without steroids or antiseizure medications

• Hormone receptor status:

  • Not specified

PATIENT CHARACTERISTICS:

Sex

• Female

Menopausal status

• Not specified

Performance status

• SWOG 0-2

Life expectancy

• Not specified

Hematopoietic

• Absolute neutrophil count ≥ 1,500/mm^3
• Platelet count ≥ 100,000/mm^3
• Hemoglobin ≥ 10 g/dL

Hepatic

• Bilirubin ≤3.0 mg/dL
• AST and ALT ≤ 2.5 times upper limit of normal

Renal

• Creatinine ≤ 1.5 mg/dL

Other

• Not pregnant or nursing
• Fertile patients must use effective contraception
• No serious systemic disorder that would preclude study compliance
• No history of another malignancy except curatively treated carcinoma of the cervix or basal cell or squamous cell skin cancer in complete remission
• No unresolved bacterial infection requiring antibiotic treatment
• No known HIV-1 positivity

PRIOR CONCURRENT THERAPY:

Biologic therapy

• At least 3 weeks since prior biologic therapy

Chemotherapy

• Prior adjuvant chemotherapy allowed

• Prior adjuvant or neoadjuvant taxane-based therapy or taxane therapy for metastatic disease allowed

  • Patient must have failed therapy within 2 years after completion of treatment

• At least 3 weeks since prior chemotherapy

• No more than 2 prior cytotoxic chemotherapy regimens for metastatic disease

• No prior gemcitabine hydrochloride

• No other concurrent chemotherapy

Endocrine therapy

• See Disease Characteristics

• At least 2 weeks since prior and no concurrent hormonal therapy

  • Must have documented disease progression during prior hormonal therapy

Radiotherapy

• See Disease Characteristics
• At least 4 weeks since prior radiotherapy and recovered
• No concurrent radiotherapy

Surgery

• At least 3 weeks since prior surgery

Other

• At least 3 weeks since prior investigational therapy

• At least 1 week since prior soy supplements (e.g., soy-based pills, liquids, or concentrates)

  • Dietary soy as part of a meal (e.g., tofu) allowed once a week

• No concurrent nutritional supplements, herbal agents, or high doses of antioxidants (e.g., vitamins C, D, or E) that may interact with, antagonize, alter, or imitate the potential effects of gemcitabine hydrochloride or genistein

  • A single daily multivitamin is allowed

• No other concurrent immunotherapy

• No other concurrent experimental medication

• Concurrent anticoagulants, appetite stimulants, and replacement steroids allowed

Although the study is designed to accrue 18 response evaluable participants in the first stage, the decision was made to close the study after 17 patients because of lack of efficacy.