Psoriasis, a proof-of-principle condition for immune-mediated inflammatory disorders: perspectives toward optimal clinical trial design

Therapeutic agents with a putative anti-inflammatory mode of action are increasingly being pilot tested in psoriasis, a chronic inflammatory systemic disease. This is because the psoriasis patient contributes a number of advantages to trial design and execution (e.g., high disease prevalence, homogenous patient characteristics, skin manifestation that supports quick and easy quantification and viable placebo controls). Trial design for psoriasis is relatively standardized. Chronic plaque-type psoriasis usually follows a stable clinical course and also has well-accepted inclusion and exclusion criteria. Since psoriasis disease activity is characterized by lesions and percentage of the body area affected, there are multiple acceptable study end points that afford quantification of therapeutic impact, including quality of life, in the absence of a need for surrogate or biomarkers. Limitations of the psoriasis clinical trial framework are also apparent (e.g., multiple psoriasis phenotypes or capacity to evaluate across the complete disease severity spectrum), which means the population is not broadly applicable to all clinical trials destined to study agents that might impact psoriasis and/or systemic inflammation. Thus, psoriasis is a proof-of-principle condition with multiple opportunities for further research in developing potential treatments for a larger proportion of the population with psoriasis and other immune-mediated inflammatory disorders.