RATIONALE: Licorice root extract contains ingredients that may slow the growth of tumor cells. Drugs used in chemotherapy, such as docetaxel, work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. Giving licorice root extract together with docetaxel may be an effective treatment for prostate cancer.

PURPOSE: This phase II trial is studying the side effects and how well giving licorice root extract together with docetaxel works in treating patients with metastatic prostate cancer that did not respond to hormone therapy.

• PSA normalization or decline of 50%

OBJECTIVES:

Primary

• Determine the efficacy and toxicity of licorice root extract in combination with docetaxel in patients with hormone-refractory metastatic prostate cancer.

Secondary

• Determine the ability of licorice root extract to alter surrogate markers of estrogen activity and cytotoxicity in these patients.

OUTLINE: Patients receive docetaxel IV over 1 hour on day 1 and oral licorice root extract 3 times a day on days 1-21. Treatment repeats every 21 days in the absence of disease progression or unacceptable toxicity.

After completion of study treatment, patients are followed periodically.

PROJECTED ACCRUAL: A total of 46 patients will be accrued for this study.

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