study of Apremilast (CC-10004) in Adults with in Psoriatic Arthritis

• Diagnosis of psoriatic arthritis (Moll and Wright Criteria), including symmetrical or asymmetrical peripheral joint involvement for at least 6 months • Active psoriatic arthritis at the time of screening and baseline as defined by: 3 or more swollen joints AND 3 or more tender joints • Negative rheumatoid factor (RF) • If using methotrexate, be on methotrexate for at least 168 days (24 weeks) and be on a stable dose for at least 56 days prior to screening and throughout the study • If using oral corticosteroids, be on a stable dose of prednisone ≤ 10 mg/day or equivalent for at least 28 days prior to screening and throughout the study • If using nonsteroidal anti-inflammatory drug (NSAID) therapy, be on a stable dose for at least 14 days prior to screening and throughout the study • Must meet the following laboratory criteria: - Hemoglobin ≥ 9 g/dL - Hematocrit ≥ 27% - White blood cell (WBC) count ≥ 3000/μL (≥ 3.0 X 10^9/L) and < 20,000/μL (< 20 X 10^9/L) - Neutrophils ≥ 1500 /μL (≥ 1.5 X 10^9/L) - Platelets ≥ 100,000 /μL (≥ 100 X 10^9/L) - Serum creatinine ≤ 1.5 mg/dL (≤ 132.6 μmol/L) - Total bilirubin ≤ 2.0 mg/dL - Aspartate transaminase (AST [serum glutamic oxaloacetic transaminase, SGOT]) and alanine transaminase (ALT [serum glutamate pyruvic transaminase, SGPT]) ≤ 1.5x upper limit of normal (ULN) • Females of childbearing potential (FCBP) must have a negative urine pregnancy test at screening (Visit 1). In addition, sexually active FCBP must agree to use TWO adequate forms of contraception while on study medication. A FCBP must agree to have pregnancy tests every 28 days while on study medication • Males (including those who have had a vasectomy) must agree to use barrier contraception (latex condoms) when engaging in reproductive sexual activity with FCBP while on study medication and for at least 84 days after taking the last dose of study medication

History of any clinically significant cardiac, endocrinologic, pulmonary, neurologic, psychiatric, hepatic, renal, hematologic, immunologic, or other major diseases • Any condition, including the presence of laboratory abnormalities, which places the subject at unacceptable risk if he/she were to participate in the study or confounds the ability to interpret data from the study • Pregnant or lactating female • History of active Mycobacterium tuberculosis infection (any subspecies) within 3 years prior to the screening visit. Infections that occurred > 3 years prior to entry must have been effectively treated. • History of incompletely treated latent Mycobacterium tuberculosis infection (as indicated by a positive Purified Protein Derivative [PPD] skin test or in vitro test [T SPOT®.TB, QuantiFERON Gold®]) • Clinically significant abnormality on the chest x-ray (CXR) at screening • Current erythrodermic, guttate, or pustular forms of psoriasis • History of infected joint prosthesis within the past 5 years • Systemic therapy for psoriasis and/or psoriatic arthritis (except for methotrexate, ≤ 10 mg/day prednisone or equivalent, and NSAIDs) including, but not limited to, sulfasalazine, leflunomide, chloroquine, hydroxychloroquine, gold compounds, parenteral corticosteroids (including intra-articular), penicillamine, cyclosporine, oral retinoids, mycophenolate mofetil, thioguanine, hydroxyurea, sirolimus, tacrolimus, azathioprine, and fumaric acid esters within 28 days of randomization and throughout the study • Topical therapy for the treatment of psoriasis including, but not limited to topical steroids, topical vitamin A or D analog preparations, tacrolimus, pimecrolimus, or anthralin within 14 days of randomization (Note: Topical background therapy for treatment of psoriasis is allowed, except within 24 hours of a study visit, as follows: mild or moderate potency corticosteroids for treatment of the palms, face, scalp, axillae, plantar surfaces, and groin in accordance with the manufacturer’s suggested usage. Nonmedicated emollients [eg, Eucerin®] and tar shampoo are also allowed.) • Phototherapy (ultraviolet light A [UVA], narrow-band ultraviolet light B [NB-UVB], psoralens and long-wave ultraviolet radiation [PUVA]) within 28 days prior to randomization • Etanercept use within 56 days prior to randomization • Adalimumab, efalizumab, or infliximab use within 84 days prior to randomization • Alefacept use within 168 days (24 weeks) prior to randomization • Use of intra-articular corticosteroids within 28 days prior to randomization • Use of any investigational medication within 28 days prior to randomization or 5 half-lives if known (whichever is longer) • Any clinically significant abnormality on 12-lead electrocardiogram (ECG) at screening • High-risk factor(s) for, or a history of, human immunodeficiency virus (HIV), hepatitis B, or hepatitis C virus infection • History of malignancy within previous 5 years (except for treated basal-cell skin carcinoma(s) and/or fewer than 3 treated squamous-cell skin carcinomas) • Evidence of skin conditions at the time of screening visit that would interfere with evaluations of the effect of study medication on psoriasis