Mass General - Division of Clinical Research

Subjects must satisfy the following criteria to be enrolled in the study: 1. Subject must be male or female, ≥18 years of age at the time of signing the informed consent form (ICF). 2. Subject must have a diagnosis of chronic plaque psoriasis for at least 6 months prior to signing the ICF. 3. Subject must have a diagnosis of mild to moderate plaque psoriasis at both Screening and Baseline. 4. Subject must be inadequately controlled with or intolerant of at least one topical therapy at both Screening and Baseline. 5. Subject must be in good health (except for psoriasis) as judged by the investigator, based on medical history, physical examination, clinical laboratories, and urinalysis. 6. Subject must meet laboratory criteria. 7. Subject has not had prior exposure to biologics for the treatment of psoriatic arthritis or psoriasis, or any other condition that could impact the assessment of psoriasis.

The presence of any of the following will exclude a subject from enrollment: 1. Subject has any significant medical condition, laboratory abnormality, or psychiatric illness that would prevent the subject from participating in the study. 2. Subjects has any condition, including the presence of laboratory abnormalities, which would place the subject at unacceptable risk if he/she were to participate in the study. 2. Subject has hepatitis B surface antigen positive at Screening. 3. Subject has active tuberculosis (TB) or a history of incompletely treated TB. 4. Subject has history of positive human immunodeficiency virus (HIV), or has congenital or acquired immunodeficiency (eg, common variable immunodeficiency disease). 5. Subject has hepatitis B surface antigen or anti-hepatitis C antibody positive at Screening. 6. Subject has prior history of suicide attempt at any time in the subject's life time or major psychiatric illness requiring hospitalization within the last 3 years prior to signing the informed consent. 7. Subject has current or planned concurrent use of therapies that may have a possible effect on psoriasis during the course of the treatment phase of the trial. 8. Use of any investigational drug beginning 4 weeks prior to randomization, or 5 pharmacokinetic/pharmacodynamic half-lives, if known (whichever is longer). 9. Subject had prior treatment with apremilast.