The purpose of this study is to determine the effects (good and bad) that mifepristone has on patients with androgen independent prostate cancer.

Patients will receive mifepristone, 200mg orally once a day. One treatment cycle is 28 days long. Patients will remain on treatment unless their cancer gets worse or they develop intolerable side effects.

At the end of each cycle a physical examination, routine blood tests, and hormone levels will be performed.

After every 3 cycles, one or more of the following will be performed: bone scan, chest x-ray, CT scan or MRI.

Inclusion Criteria:

• Histologic documentation of adenocarcinoma of the prostate
• Bone metastasis(es) by bone scan or cat scan
• Clinical, biochemical, or radiographic progression after primary androgen ablation with either orchiectomy or gonadotropin releasing hormone analog therapy.
• One prior chemotherapy treatment is allowed.
• > 3 weeks since major surgery
• > 4 weeks since radiotherapy
• > 8 weeks since prior strontium-89 or samarium 153
• ECOG performance status 0 or 1
• Absolute neutrophil count (ANC) > 1,500/ul
• Platelets > 100,000/ul
• Bilirubin < 1.5 x upper limit of normal (ULN)
• AST or ALT < 3 x ULN
• Creatinine < 1.5 x ULN
• Electrolytes within 10% of normal range
• Serum testosterone < 50ng/dL
• Prostate-specific antigen (PSA) > 5.0ng/ml

Exclusion Criteria:

• Concomitant therapy with corticosteroids
• Chemotherapy within 28 days
• Currently active second malignancy other than non-melanoma skin cancer
• Baseline adrenal insufficiency requiring long-term steroids