Age-dependent interaction between sex and geographic ultraviolet index in melanoma risk

Ultraviolet (UV) exposure may not affect melanoma development equally in different sexes and ages. Whether and how these factors interact with each other in relation to melanoma risk is unknown.This study attempts to estimate interactions among UV index (UVI), sex, and age in melanoma risk.Melanoma incidence data were collected from 42 cancer registries. Geographic UVI was collected from local satellite stations. Negative binomial regression models were used to estimate the impact of each risk factor and their interactions.Sex, UVI, and age, as well as interactions between any 2 of these factors, were significantly associated with melanoma risk. In younger age groups, female sex is an independent risk factor for melanoma that is not affected by ambient UV exposure. In older age groups, however, female sex interacts with UV exposure as a risk factor, exhibiting a protective effect. The switching age category is 45 to 49, which correlates with dramatic hormonal changes.The interaction between sex and UVI is measured at an ecologic level.The interaction between sex and UVI is age dependent. Female sex is an independent risk factor for early-onset melanoma, but female sex also protects against UV-associated melanoma in older age groups.