Inclusion Criteria

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