Study of Ruxolitinib (INCB018424) Administered Orally to Patients With Androgen Independent Metastatic Prostate Cancer

Inclusion Criteria: * Diagnosed with radiographically-documented metastatic prostate cancer that has progressed while receiving androgen-suppressive therapy in the form of a bilateral orchiectomy or Gonadotropin-Releasing Hormone (GnRH) agonist (eg, leuprolide, goserelin). * Patients must demonstrate evidence of progressive disease based on 1 of the following criteria: 1) Progressive measurable disease, or 2) Progressive rise in prostate-specific antigen (PSA) level (2 consecutive rises from a prior reference level), or 3) Development of new lesions on bone scan. * If receiving a GnRH agonist as primary hormonal therapy, the serum testosterone level must be ≤ 50 ng/mL. * Must have received and progressed during or following 1 prior chemotherapy regimen for metastatic disease (not including an anti-androgen or ketoconazole); or, must have discontinued prior systemic therapy because of poor tolerance or other adverse effects; or, must have refused chemotherapy treatment. Patients having undergone more than 1 prior chemotherapy regimen may be admitted at the discretion of the sponsor. * Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 2. * Baseline serum PSA level of ≥ 10 ng/mL Exclusion Criteria: * Received any anti-cancer medications in the 30 days before receiving their first dose of study medication except for GnRH agonists and bisphosphonates. * Any unresolved toxicity greater than or equal to Grade 2 from previous anti-cancer therapy, except for stable chronic toxicities not expected to resolve, such as peripheral neurotoxicity.