Association between cutaneous melanoma incidence rates among white US residents and county-level estimates of solar ultraviolet exposure.

BACKGROUND Recent US studies have raised questions as to whether geographic differences in cutaneous melanoma incidence rates are associated with differences in solar ultraviolet (UV) exposure. OBJECTIVES We sought to assess the association of solar UV exposure with melanoma incidence rates among US non-Hispanic whites. METHODS We assessed the association between county-level estimates of average annual solar UV exposure for 1961 to 1990 and county-level melanoma incidence rates during 2004 to 2006. We used Poisson multilevel mixed models to calculate incidence density ratios by cancer stage at diagnosis while controlling for individuals' age and sex and for county-level estimates of solar UV exposure, socioeconomic status, and physician density. RESULTS Age-adjusted rates of early- and late-stage melanoma were both significantly higher in high solar UV counties than in low solar UV counties. Rates of late-stage melanoma incidence were generally higher among men, but younger women had a higher rate of early-stage melanoma than their male counterparts. Adjusted rates of early-stage melanoma were significantly higher in high solar UV exposure counties among men aged 35 years or older and women aged 65 years or older. LIMITATIONS The relationship between individual-level UV exposure and risk for melanoma was not evaluated. CONCLUSIONS County-level solar UV exposure was associated with the incidence of early-stage melanoma among older US adults but not among younger US adults. Additional studies are needed to determine whether exposure to artificial sources of UV exposure or other factors might be mitigating the relationship between solar UV exposure and risk for melanoma.