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.

Keywords: UV index; UVI; age-standardized rates; gender difference; melanoma; sex.

Figure 1. Melanoma incidence rates: Linear regression of log-transformed age-standardized melanoma incidence rates from 31 registries with average local daily UVI

A, males; B, females. Solid lines represent the fitted line; shaded areas represent 95% confidence interval.

Figure 2. Melanoma rates and age: Levels of rate-UVI association increase with age in men but not in women

Five-year age-specific rates were calculated for each registry for each gender, association of these rates (log-transformed) with UVI was analyzed to obtain Pearson’s ρ for each age category. These ρ values were plotted against age categories. Squares and solid line: ρ for males in each age categories and the regression line. Filled circles and dotted line: ρ for females in each age categories and the regression line.