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Vitiligo and skin cancer: is it a question of ethnicity?

and safety of brodalumab in obese vs. nonobsese patients with psoriasis. The authors pooled the data of two duplicate phase III trials and evaluated skin clearance and safety in patients who received brodalumab 210 mg every 2 weeks, patients who received ustekinumab and patients who switched at 16 weeks from ustekinumab to brodalumab 210 mg every 2 weeks because of a lack of efficacy. They concluded that brodalumab 210 mg every 2 weeks was effective regardless of obesity in patients with moderate-to-severe psoriasis at 12 and 52 weeks. ‘One-size-fits-all medicine’ is a rarely kept promise. Most medical therapies administered to large groups of participants only help a subset of patients. The usual question of interest is whether the treatment effect varies among disease or patient characteristics. In the field of psoriasis, 30–40% of patients with severe psoriasis are overweight or obese. Obesity has been associated with a lower persistence of some biologics owing to a lack of efficacy and adverse events. Thus, it is crucial to obtain efficacy and safety results for obese patients with psoriasis when assessing a new therapeutic target, which is exactly what Hsu et al. did. In randomized controlled trials (RCTs), subgroup analyses are generally performed in addition to the main analysis to assess the treatment effect in subpopulations. Some analyses are planned at protocol stages and others not (i.e. a post hoc analysis, as carried out by Hsu et al.). In line with the CONSORT statement, subgroup analyses should be prespecified, i.e. planned in the protocol and/or registration form. Prespecification means that reporting of the results of only some subgroups can be avoided. In addition, subgroup analyses face different methodological issues, such as multiple testing, which leads to an increased risk of a false-positive result. In contrast, subgroup analyses require the data to be divided into smaller datasets, thus reducing the power of detecting a treatment effect, leading to an increased risk of a false-negative result. Not considering such issues may contribute to a lack of consistency in the analysis and interpretation of subgroup analyses. Subgroup analyses need to be tested for interaction, i.e. a test to determine whether the effects of study treatments vary significantly between patient subgroups. In RCTs power calculations can be also performed with prespecified subgroup analyses in mind. Thus, prespecified and limited numbers of subgroup analyses are better than post hoc and multiple tests analyses. How to choose the right subgroup analyses to describe the evolution of psoriasis under a therapy is a problem that still needs to be solved. Many characteristics are relevant in clinical practice: age, sex, severity of the disease, type of psoriasis, previous therapeutic lines, obesity, psoriatic arthritis, and so on. What are the minimal subgroup sets of interests in the field of psoriasis? COMET (Core Outcome Measures in Effectiveness Trials) is an international initiative involving patients, researchers, physicians and a regulatory body, which aims to develop and implement a minimal set of outcomes that should be measured and reported in all clinical trials of a specific condition. One of the aims of this initiative is to be able to pool data in systematic reviews thanks to homogeneous outcomes between trials. It is not possible to pool subgroup analysis data if subgroup analyses are heterogeneous. We suggested that ‘COre SUBgroup SETs’ (COSUBSET) becomes a research subgroup of COMET. There is a need to define core subgroup analysis sets for psoriasis that can be shared by all RCTs. Lastly, subgroup analyses are also needed for researchers who performed systematic reviews and meta-analysis. Hsu et al. not only performed a pooled analysis, but also provided separate data for each trial, allowing for future systematic reviews and meta-analyses. By assessing the efficacy of brodalumab in an obese population with severe psoriasis, Hsu et al. have provided a first step in guiding treatment strategy depending on the patients’ characteristics. The next steps will be to define core subgroup sets in the field of psoriasis, which will be systematically planned, analysed, presented and interpreted in RCTs.