Phase 3b Safety and Efficacy Study of Apremilast to Treat Moderate to Severe Plaque-plaque Psoriasis

This is a phase 3b, multicenter, randomized, placebo-controlled, double-blind, double-dummy, study of the efficacy and safety of apremilast, etanercept, and placebo, in adults with moderate to severe plaque psoriasis. 250 participants will be randomized 1:1:1 to the three treatment groups. All subjects will receive both tablets and injections through Week 16. The study will consist of four phases: * Screening Phase - up to 35 days * Double-blind Placebo-controlled Phase - Weeks 0-16 * Apremilast Extension Phase - Weeks 16-104 * Post-treatment Observational Follow-up Phase During the double-blind, placebo-controlled phase, subjects will receive treatment with one of the following: * apremilast (APR) 30 mg tablets orally twice a day (BID) plus once weekly (QW) evaluator/subject-blinded subcutaneous (SC) saline (placebo) injections (1 mL x 2 injections SC), or * etanercept (ETN) 50 mg evaluator/subject-blinded subcutaneous (SC) once weekly (QW) injections (2 x 25 mg) plus placebo tablets orally twice a day (BID), or * placebo tablets and evaluator/subject-blinded subcutaneous (SC) saline (placebo) injections. All subjects will be asked to participate in a 4-week Post-treatment Observational Follow-up Phase either upon completion of the study or upon discontinuation of investigational product for those subjects who terminate the study early.