This landmark trial randomized 1195 patients with metastatic hormone resistant prostate cancer and who had already received docetaxel chemotherapy to either abiraterone 1gm orally once daily plus prednisone 5 mg twice daily, or placebo. Abiraterone is an inhibitor of cytochrome P450 an enzyme that is critical in androgen synthesis by the adrenals, testes and within the prostate. The median patient age was 69, with 28% above 75. The main site of metastases was bone (89%) and then lymph nodes (45%0 then liver (11%). The median PSA was 129 ng/mL and 90% had good performance status. At 12.8 months median follow up the abiraterone group had longer overall survival (14.8 v 10.9 months), and all secondary endpoints were also better – progression free survival, PSA progression and PSA response. The adverse effects of abiraterone were mostly related to mineralocorticoid excess (which is why prednisone must be given with it) including fluid retention, hypokalemia and high blood pressure. The rate of discontinuation was low however. Also non fatal cardiac events were non statistically significant higher in abiraterone group including tachycardia and atrial fibrillation. Other side effects were nausea, constipation, back pain, bone pain and arthralgia.