DISEASE CHARACTERISTICS:

• Histologically or cytologically confirmed breast cancer

  • Refractory metastatic disease

• Measurable disease

  • At least 1 unidimensionally measurable lesion ≥ 20 mm by conventional techniques OR ≥ 10 mm by spiral CT scan
• Must have received 1, and only 1, prior chemotherapy regimen for metastatic disease
• Patients overexpressing HER2/neu antigen must have received a prior trastuzumab (Herceptin^®)-containing regimen
• No known brain metastases

• Hormone receptor status:

  • Not specified

PATIENT CHARACTERISTICS:

Age

• 18 and over

Sex

• Male or female

Menopausal status

• Not specified

Performance status

• ECOG 0-2

Life expectancy

• At least 12 weeks

Hematopoietic

• WBC ≥ 3,000/mm^3
• Absolute neutrophil count ≥ 1,500/mm^3
• Platelet count ≥ 100,000/mm^3

Hepatic

• Bilirubin normal
• AST and ALT ≤ 2.5 times upper limit of normal

Renal

• Creatinine normal OR
• Creatinine clearance ≥ 60 mL/min

Cardiovascular

• No uncontrolled congestive heart failure
• No unstable angina pectoris
• No cardiac arrhythmia

Pulmonary

• No severe pulmonary disease requiring oxygen

Other

• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception
• No glucose-6-phosphate dehydrogenase (G6PD) deficiency
• No other uncontrolled illness
• No active or ongoing infection
• No history of allergic reaction attributed to compounds of similar chemical or biological composition to 3-AP (Triapine^®) or other study agents
• No psychiatric illness or social situation that would preclude study compliance
• No other malignancy within the past 5 years

PRIOR CONCURRENT THERAPY:

Biologic therapy

• See Disease Characteristics
• No concurrent immunotherapy
• No concurrent routine colony-stimulating factors (e.g., filgrastim [G-CSF] or sargramostim [GM-CSF])

Chemotherapy

• See Disease Characteristics
• More than 4 weeks since prior chemotherapy (6 weeks for nitrosoureas or mitomycin)
• No prior gemcitabine for metastatic disease
• No other concurrent chemotherapy

Endocrine therapy

• More than 4 weeks since prior hormonal therapy

Radiotherapy

• More than 4 weeks since prior radiotherapy
• No concurrent radiotherapy

Surgery

• Not specified

Other

• Recovered from prior therapy
• No concurrent antiretroviral therapy for HIV-positive patients
• No other concurrent investigational therapy