ObjectiveEvaluation of the efficacy and safety of guselkumab, a human monoclonal antibody targeting the interleukin-23p19 subunit, in patients with psoriatic arthritis (PsA) through 1 year.MethodsAdults who met ClASsification criteria for Psoriatic ARthritis, with active disease (≥3 swollen and ≥3 tender joints; C reactive protein ≥0.3 mg/dL) despite standard treatment (31% previously received ≤2 tumour necrosis factor inhibitors (TNFi)), were randomised (1:1:1) to guselkumab 100 mg every 4 weeks (Q4W); guselkumab 100 mg at Week0, Week4, then Q8W; or placebo with cross-over to guselkumab 100 mg Q4W at Week24 (PBO→Q4W) through Week48. Clinical efficacy through Week52 (employing non-responder imputation) and adverse events (AEs) through Week60 were evaluated.ResultsOf 381 treated patients, 90% completed the study. Numerical increases in the proportions of patients achieving ≥20% improvement in ACR criteria (ACR20) were observed post-Week24, reaching 73% (94/128) and 60% (76/127) for Q4W-randomised and Q8W-randomised patients, respectively, by Week52. Proportions of patients achieving ACR50/ACR70/skin responses and minimal/very low disease activity were maintained, as were improvements in physical function and health-related quality of life, through Week52 in guselkumab-randomised patients. Response to guselkumab was maintained in both TNFi-naïve and TNFi-experienced patients. Serious AEs and serious infections occurred in similar proportions of guselkumab Q4W-randomised (3% and 0%) and Q8W-randomised (6% and 2%) patients through Week60, with no new safety concerns versus observations through Week24. No guselkumab-treated patient and two patients receiving placebo died; no study participant developed opportunistic infection or inflammatory bowel disease.ConclusionGuselkumab provided sustained improvement across multiple clinical manifestations of PsA, maintaining a favourable benefit-risk profile, through 1 year regardless of prior TNFi exposure.