Licorice Root Extract and Docetaxel in Treating Patients With Metastatic Prostate Cancer That Did Not Respond to Hormone Therapy

DISEASE CHARACTERISTICS: Diagnosis of prostate adenocarcinoma Metastatic disease Must have failed initial hormonal therapy and have disease progression after at least one chemotherapy regimen*, meeting any of the following criteria: Progressive PSA ≥ 5 ng/mL, as evidenced by 2 separate measurements taken ≥ 2 weeks apart with the second PSA measurement greater than the first one and PSA measurement at screening greater than the first one Progressive measurable disease (e.g., changes in the size of lymph nodes or parenchymal masses or appearance of new lesions on physical examination or x-ray/CT scan) with a PSA level at screening ≥ 5 ng/mL Progressive bone metastasis (e.g., presence of new lesions on a bone scan) with a PSA level at screening ≥ 5 ng/mL NOTE: *Prior chemotherapy must include a taxane therapy, but disease progression does not have to follow taxane therapy Patients must maintain primary androgen ablation (hormonal) therapy AND experience disease progression while not receiving antiandrogen therapy PATIENT CHARACTERISTICS: ECOG performance status 0-1 Life expectancy ≥ 6 months Absolute neutrophil count ≥ 1,500/mm^3 Platelet count ≥ 100,000/mm^3 WBC ≥ 3,500/mm^3 Bilirubin ≤ 1.2 mg/dL Creatinine ≤ 1.5 mg/dL SGOT or SGPT ≤ 1.5 times upper limit of normal No other prior malignancy unless treated with curative intent and free of disease for the time period considered appropriate for the specific cancer No uncontrolled hypertension No active infections No known HIV positivity No uncontrolled medical condition that would preclude study therapy No diagnosis of major depression or suicidal ideation No problems with oral absorption PRIOR CONCURRENT THERAPY: See Disease Characteristics More than 4 weeks since prior surgery or radiotherapy and recovered At least 4 weeks since prior flutamide At least 6 weeks since prior bicalutamide No prior or concurrent herbal supplements or thiazide diuretics No other concurrent investigational or commercial agents or therapies