Although there have been advances in the treatment of patients with metastatic castrate-resistant prostate cancer (mCRPC), all patients eventually develop resistance to available therapy. Docetaxel is the accepted first-line agent followed by cabazitaxel in the post-docetaxel phase. In this study the investigators propose to evaluate BKM120, a PI3K inhibitor, with cabazitaxel in the treatment of patients with advanced prostate cancer.