Background: Docetaxel (D) in combination with prednisone (P) as first-line (1L) chemotherapy in patients (pts) with mCRPC is the current standard of care. However, treatment is not curative and D-resistant disease typically develops. Cabazitaxel (Cbz) is a novel taxane active in D-sensitive and -resistant tumor models. Clinical activity of Cbz plus P (CbzP) was demonstrated in the Phase III TROPIC study in mCRPC pts previously treated with a D-containing regimen; CbzP showed a significant overall survival (OS) benefit vs mitoxantrone plus prednisone (median OS 15.1 vs 12.7 months; HR 0.70; P < 0.0001). Therefore, it is of interest to determine if CbzP provides an OS advantage vs DP in 1L mCRPC pts. Methods: The phase III FIRSTANA study (NCT01308567) is a randomized, open-label, multinational trial in 1L mCRPC pts, designed to compare the efficacy of Cbz 25 mg/m² IV Q3W (Arm A) and Cbz 20 mg/m² IV Q3W (Arm B) vs D 75 mg/m² IV Q3W (Arm C). P 10 mg PO QD is to be given concomitantly. Pts are stratified by ECOG PS (0–1 vs 2), measurable disease (yes/no) and region (depending on availability of Cbz as 2L). Pts with ECOG PS ≤ 2, histologically/cytologically confirmed metastatic prostate adenocarcinoma, with no prior chemotherapy and with disease progression following medical or surgical castration are eligible. The primary endpoint is OS. Secondary endpoints include progression-free survival (PFS) (PCWG2 criteria), radiologic PFS, tumor response in measurable disease (RECIST 1.1), PSA response and PSA PFS, pain response and pain PFS, time to occurrence of any skeletal-related events, safety profile and health-related quality of life. Cbz pharmacokinetics and pharmacogenomics will be assessed in pt subgroups. Pts will be treated until progression, unacceptable toxicity or pt request. Planned enrollment is 1,170 pts; study size was calculated to achieve 90% power for OS. Study start was in May 2011; at January 2012, 219 pts were enrolled. The first DMC meeting recommended continuing the study without change.