Abiraterone Post Ketoconazole for Prostate Cancer

Inclusion Criteria: * Histologically confirmed adenocarcinoma of the prostate * Prior therapy with ketoconazole for castration resistant prostate cancer. Patients should demonstrate evidence of progression (see below definitions) on ketoconazole or evidence of grades 3/4 toxicities on ketoconazole. 1. Ketoconazole must have been administered for \>28 days 2. At least 27 days must elapse since last ketoconazole dose and first dose of abiraterone acetate * No prior therapy with chemotherapy for metastatic prostate cancer * Metastatic disease based on a positive bone scan or objective imaging on CT scan * Ongoing gonadal androgen deprivation therapy with LHRH analogues or orchiectomy. Patients, who have not had an orchiectomy, must be maintained on effective LHRH analogue therapy for the duration of the trial * Testosterone \< 50 ng/dL * Progressive disease after androgen deprivation: PSA evidence for progressive prostate cancer consists of a PSA level of at least 2 ng/ml which has risen on at least 2 successive occasions, at least 2 weeks apart * Patients who are receiving an antiandrogen as part of primary androgen ablation must demonstrate disease progression following discontinuation of antiandrogen * ECOG Performance Status 0-1 * Age \>18 years and able to comply with protocol requirements * Serum Creatinine ≤1.5 x ULN * Serum potassium \>3.5mmol/L * Bilirubin ≤1.5x ULN * AST and ALT ≤2.5 x ULN * Life expectancy of \>12 weeks Exclusion Criteria: * Therapy with other hormonal therapy, including any dose of megestrol acetate (Megace), finasteride (Proscar), dutasteride (Avodart) any herbal product known to decrease PSA levels (e.g., Saw Palmetto and PC-SPES), or any systemic corticosteroid within 4 weeks prior to first dose of study drug * Therapy with supplements or complementary medicines/botanicals within 4 weeks of first dose of study drug, except for any combination of the following; conventional multivitamin supplements, Selenium, Lycopene and Soy supplements * Prior radiation therapy completed \< 4 weeks prior to enrollment * Prior chemotherapy for castration resistant prostate cancer. Patients who have received chemotherapy for early stage prostate cancer (e.g. as part of a neoadjuvant or adjuvant trial) or for other malignancies are eligible provided that \>1 year has passed since the administration of the last chemotherapy dose. * Hemoglobin ≤9.0 g/dL * Any "currently active" second malignancy, other than non-melanoma skin cancer Patients are not considered to have a "currently active" malignancy, if they have completed therapy and are considered by their physician to be at least less than 30% risk of relapse over next 3 months * Blood pressure that is not controlled despite \>2 oral agents (SBP \>160 and DBP \>90 on three or more readings within the screening period) * Serum K+ \<3.5 mmoL/L on more than one reading within the screening period * NYHA Class II, NYHA Class III or IV Congestive Heart Failure * Myocardial infarction within the 6 months prior to the first dose of study drug * Serious intercurrent infections or nonmalignant medical illnesses that are uncontrolled * Concurrent therapy with drugs that are metabolized as substrates of CYP1A2, CYP2D6, or CYP2C19 and are considered by the investigators to pose a risk for drug to drug interactions