MTD was defined as highest dose level of cabazitaxel in combination with abiraterone acetate at which no more than 1 participant experienced dose limiting toxicities (DLT). DLT was defined as any of the following events related to study treatment: 1) Grade 3 or 4 non-hematological related adverse event with exception of Grade 3 fever without documented infection; Grade 3 nausea, vomiting, or diarrhea in the absence of effective maximal therapy; and Grade 3 hypersensitivity reaction in the absence of required premedication. 2) Hematological toxicity: Febrile neutropenia (fever of unknown origin ≥38.5°C with neutropenia Grade 3 or 4); Neutropenia Grade 4 lasting \>7 days; Thrombocytopenia Grade 4 or Grade 3 complicated by hemorrhage. 3) Re-treatment delay of more than 2 weeks due to delayed recovery from a toxicity related to study treatment to baseline or ≤ Grade 1 (except for alopecia). Grades were based on National Cancer Institute CommonTerminology Criteria for Adverse Events v4.03.

Prostate specific antigen (PSA) response was defined as ≥50% decrease from baseline in serum PSA levels, confirmed at least 3 weeks later. Increases of any magnitude during the first 12 weeks were ignored in determining PSA response. PSA was to be measured at baseline, every 3 weeks, throughout study period, until progression. PSA progression was defined as: -An increase of 25% above the nadir (at least 2 ng/mL), confirmed by a second PSA value at least 3 weeks apart, in participants who have achieved a ≥50% decline of PSA. -An increase in PSA by 25 % above the baseline level (at least 2 ng/mL), confirmed by a second PSA value at least 3 weeks apart, in participants who have not achieved a ≥50% decline of PSA.