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

ABSTRACT

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.