INTRODUCTION: Platelet-derived growth factor receptor-α (PDGFRα) is expressed in primary prostate adenocarcinoma and in associated skeletal metastases. Olaratumab is a fully human monoclonal antibody that binds PDGFRα and blocks downstream signalling. This phase II study assessed the efficacy and safety of olaratumab in combination with mitoxantrone and prednisone (M/P) versus M/P alone in patients with metastatic castration-resistant prostate cancer (mCRPC) who progressed after docetaxel. METHODS: Patients were randomised to receive 21-d cycles of olaratumab (15 mg/kg, Days 1 and 8) plus mitoxantrone (12 mg/m2, Day 1) and prednisone (5 mg, twice daily) or M/P alone. Progression-free survival (PFS) was the primary end-point. Secondary end-points included overall survival (OS), safety, and circulating tumour cell (CTC) counts. RESULTS: A total of 123 patients were randomised, 63 to olaratumab + M/P and 60 to M/P. Median PFS was 2.3 months for olaratumab + M/P and 2.4 months for M/P (hazard ratio [HR] = 1.29; 95% confidence interval [CI] = 0.87-1.90). Median OS was 14.2 months for olaratumab + M/P and 12.8 months for M/P (HR = 1.08; 95% CI = 0.72-1.61). Both treatment arms had similar toxicity profiles; neutropenia (24% versus 15%), anaemia (13% versus 14%) and fatigue (11% versus 9%) (olaratumab + M/P versus M/P, respectively) were the most common grade ≥3 events. High CTC count was associated with poorer OS in both arms. Patients with very high cell counts (>37 cells/7.5 ml) exhibited improved OS with olaratumab + M/P (interaction P = 0.043). CONCLUSIONS: Olaratumab + M/P had an acceptable safety profile but did not improve the efficacy of M/P chemotherapy. Further study with selected patient populations and earlier in the disease course might be considered.

Centrum Onkologii Instytut im Marii Sklodowskiej Curie Warsaw Poland

CHU Sart Tilman University of Liège Liège Belgium

Clinica Universidad De Navarra Pamplona Spain

Department of Urologie Universitätsmedizin Rostock Rostock Germany

Department of Urology and Uro Oncology University Hospital Cologne Cologne Germany

Department of Urology General University Hospital And 1st Faculty of Medicine Charles University Prague Czech Republic

Department of Urology Josa Andras Teaching Hospital Nyiregyhaza Hungary

Department of Urology University of Freiburg Freiburg Germany

Eli Lilly and Company Basingstoke United Kingdom

Eli Lilly and Company Bridgewater NJ USA

Eli Lilly and Company Indianapolis IN USA

Eli Lilly and Company NY USA

Medical Oncology Department Hospital 12 De Octubre Madrid Spain

Medical Oncology Department Santa Chiara Hospital Trento Italy

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