Siltuximab is a chimeric, anti-interleukin-6 monoclonal antibody with potential therapeutic benefit in castration-resistant prostate cancer (CRPC) patients. We assessed the safety and tolerability of siltuximab in combination with docetaxel, the pharmacokinetics of docetaxel alone and with siltuximab, and the efficacy and pharmacodynamics of siltuximab plus docetaxel.