Caution Required in Interpreting Primary Care Vitiligo Skin Cancer Data.

I read with interest the article “Risk of Melanoma and Non-melanoma Skin Cancer in People with Vitiligo: United Kingdom Population-Based Cohort Study” by Ferguson et al., 2023 Ferguson J. Eleftheriadou V. Nesnas J. Risk of melanoma and nonmelanoma skin cancer in people with vitiligo: United Kingdom population-based cohort study [e-pub ahead of print]. J Invest Dermatol. 2023; (accessed XXX)https://doi.org/10.1016/j.jid.2023.04.013 Abstract Full Text Full Text PDF Scopus (1) Google Scholar and was pleased to see research taking place on this important topic; however, I was concerned to see that a major limitation of the dataset was not discussed. This article uses a large primary care dataset of 15,156 vitiligo cases matched to 60,615 controls to show that patients with vitiligo are at a reduced risk of skin cancer compared with those without vitiligo and concludes to reassure patients with vitiligo that their risk of skin cancer is lower (adjusted hazard ratio = 0.62, 95% confidence interval = 0.52−0.75, P < 0.001). However, the dataset has inherent selection bias. For example, a patient with less pigmented skin has less cosmetic morbidity as a result of their vitiligo ( Alikhan et al., 2011 Alikhan A. Felsten L.M. Daly M. Petronic-Rosic V. Vitiligo: a comprehensive overview part I. Introduction, epidemiology, quality of life, diagnosis, differential diagnosis, associations, histopathology, etiology, and work-up. J Am Acad Dermatol. 2011; 65: 473-491 Abstract Full Text Full Text PDF PubMed Scopus (461) Google Scholar ) and therefore are less likely to attend primary care regarding their condition and in turn documented in their medical records. This results in selection bias where patients at the highest risk of skin cancer (i.e., Fitzpatrick skin type I) may be inadvertently excluded. Thus, it is not surprising to see that the biased vitiligo cohort is at a lower risk of skin cancer than the age- and sex-matched control group. Ferguson et al., 2023 Ferguson J. Eleftheriadou V. Nesnas J. Risk of melanoma and nonmelanoma skin cancer in people with vitiligo: United Kingdom population-based cohort study [e-pub ahead of print]. J Invest Dermatol. 2023; (accessed XXX)https://doi.org/10.1016/j.jid.2023.04.013 Abstract Full Text Full Text PDF Scopus (1) Google Scholar performed subgroup analysis adjusting for ethnicity by grouping patients into a White or non-White ethnic group, but this is a poor proxy for skin type and skin cancer risk, which can vary significantly within these groups. Of interest, there was no significant difference in skin cancer risk between the non-White patients with vitiligo and the controls, but this subgroup analysis is underpowered owing to the low skin cancer counts in the non-White subgroups (9 of 3,179 vitiligo cases vs. 66 of 12,663 matched controls; adjusted hazard ratio = 0.97, 95% confidence interval = 0.45–2.06).