In a phase 2b study, 12 weeks of treatment with an oral formulation of tofacitinib resulted in clinical improvement compared with placebo in patients with moderate-to-severe plaque psoriasis.10 In a proof-of-concept study with the JAK1/2 inhibitor INCB018424 applied topically in a cream formulation for 4 weeks, the mean total lesion score (scale of 0–4 for erythema, scaling and thickness; total score range 0–12) at week 4 decreased from baseline by 32% with vehicle daily or twice daily; 53% with 1.0% INCB018424 daily; and 54% with 1.5% INCB018424 twice daily. This evidence concerns the gene JAK1 and Erythema.