Melanoma Incidence by Sex, Indoor Tanning, and Body Site

Abstract

To the Editor We read with tremendous enthusiasm the original investigation by Dr Adamson and colleagues 1 demonstrating the prominence of high diagnostic scrutiny in melanoma incidence and the necessity to take seriously the role it plays in melanoma mortality. What intrigued us is the study's conclusion that UV radiation exposure has a weak association with melanoma incidence in the US, shattering the long-standing perception of UV radiation as a formidable risk factor. If the conclusion holds true, it will alleviate the unease to some extent and downsize the magnitude of risk factors, among which UV radiation has been the most widely accepted and biggest culprit for melanoma.The study by Dr Adamson and colleagues 1 was extensively controlled for important confounders, including age, UV radiation proxies, and diagnostic scrutiny proxies. However, we believe there are 3 confounders that should be highlighted by this outstanding original investigation. First, the difference by sex should be addressed. A large observational study 2 that collected data on melanoma from 31 international cancer registries and cross-validated these global data against a second data set from 42 US states showed that melanoma incidence among male individuals was significantly associated with UV radiation exposure, but among female individuals, it was not. The significant association in men and the nonassociation in women were validated among a US population of White individuals. Furthermore, the high incidence of melanoma among men has been validated by another retrospective cohort study of 265 302 cases of melanoma. 3 The second confounder that should be highlighted is indoor tanning. In the setting of high rates of indoor tanning use among young White (not Hispanic) individuals, a systematic review and meta-analysis 4 found a significant association between indoor tanning and a higher risk of melanoma.Indoor tanning may be a potential risk factor when 2 areas are at opposite extremes of UV radiation exposure, yet incidence is at similar levels.The third confounder is the body site on which the melanoma occurs. A large, population-based, prospective cohort study of 161 540 individuals 5 found a significant association of UV radiation exposure or indoor tanning and melanoma on the lower extremities.We regard the findings of Dr Adamson and colleagues 1 to be groundbreaking. However, if the confounders that we enumerated were to supplement this investigation, its findings would be more targeted and more useful to researchers designing randomized clinical trials and to public health officials developing relevant health policies.