Sex differences in the association of cutaneous melanoma incidence rates and geographic ultraviolet light exposure

Background Cutaneous melanoma (CM) incidence rates continue to increase, and the reasons are unknown. Previously, we reported a unique age-specific sex difference in melanoma that suggested additional causes other than solar ultraviolet (UV) radiation. Objective This study attempted to understand whether and how UV radiation differentially impacts the CM incidence in men and women. Methods CM data and daily UV index (UVI) from 31 cancer registries were collected for association analysis. A second dataset from 42 US states was used for validation. Results There was no association between log-transformed female CM rates and levels of UVI, but there was a significant association between male rates and UVI and a significant association between overall rates and UVI. The 5-year age-specific rate–UVI association levels (represented by Pearson's coefficient ρ) increased with age in men, but age-specific ρ levels remained low and unchanged in women. The significant rate–UVI association in men and nonassociation in women was validated in a population of white residents of the United States. Limitations Confounders, including temperature and latitude, are difficult to separate from UVI. Conclusions Ambient UVI appears to be associated with melanoma incidence in males but not in females.