Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically confirmed adenocarcinoma of the prostate

- Metastatic or recurrent disease

- No curative standard therapy exists

- Hormone-refractory disease

- Evidence of prostate-specific antigen (PSA) progression during androgen ablation
therapy, including medical or surgical castration

- Documented PSA progression after completion of prior peripheral
anti-androgens

- At least a 25% increase (≥ 5 ng/mL) over a reference value PSA with 2
consecutive rising PSAs taken ≥ 1 week apart

- Castrate level of testosterone ≤ 1.7 nmol/L for patients on medical
androgen ablation

- Patients receiving luteinizing hormone-releasing hormone agonist
therapy must continue this treatment during study participation

- PSA ≥ 10 ng/mL at the time of study entry

- Primary tumor tissue (paraffin embedded) must be available for immunohistochemistry

- Minimal symptomatic disease

- No requirement for morphine or equivalent dose > 30 mg/day to control pain

- No known brain metastases

PATIENT CHARACTERISTICS:

Age

- 18 and over

Performance status

- ECOG 0-1

Life expectancy

- At least 12 weeks

Hematopoietic

- Absolute granulocyte count ≥ 1,500/mm^3

- Platelet count ≥ 100,000/mm^3

- No evidence of bleeding diathesis

Hepatic

- Bilirubin normal

- AST and ALT ≤ 2.5 times upper limit of normal

Renal

- Serum creatinine normal OR

- Creatinine clearance ≥ 60 mL/min

Cardiovascular

- No myocardial infarction within the past 6 months

- No congestive heart failure

- No unstable angina

- No active cardiomyopathy

- No unstable ventricular arrhythmia

- No uncontrolled hypertension

Other

- No serious infection

- No active peptic ulcer disease

- No upper gastrointestinal or other condition that would preclude study compliance
with oral medication

- No uncontrolled psychotic disorder

- No history of allergic reaction attributed to compounds of similar chemical or
biologic composition to sorafenib or other study agents

- No other serious illness or medical condition that would preclude study participation

- No other malignancy within the past 5 years except adequately treated non-melanoma
skin cancer or other curatively treated solid tumor

PRIOR CONCURRENT THERAPY:

Biologic therapy

- Concurrent prophylactic filgrastim (G-CSF), sargramostim (GM-CSF), or other growth
factors allowed for the management of adverse events only

Chemotherapy

- No prior chemotherapy

- No other prior cytotoxic chemotherapy

Endocrine therapy

- See Disease Characteristics

- Concurrent steroids allowed provided there has been no increase in steroid
requirements within the past 4 weeks AND no increase in dose is planned

Radiotherapy

- At least 4 weeks since prior external-beam radiotherapy except low-dose
non-myelosuppressive radiotherapy

- Concurrent low-dose non-myelosuppressive palliative radiotherapy allowed

Surgery

- Not specified

Other

- No prior investigational anticancer agents

- No concurrent therapeutic anticoagulation

- Concurrent prophylactic low-dose warfarin for venous or arterial access devices
allowed

- No concurrent combination antiretroviral therapy for HIV-positive patients

- No other concurrent anticancer therapy

- No other concurrent investigational therapy

- No concurrent grapefruit juice

- Concurrent bisphosphonates allowed