Solar radiation and melanoma epidemiology in Norway: Epidemiological data argue against a negative impact of sun exposure for certain types of melanoma

Norway has one of the highest melanoma incidences in the World, despite the low fluences of ultraviolet radiation. This has been partially explained by the phenotypic characteristics of the population. However, the correlation between melanoma and sun exposure is not yet fully understood. In the present work, we performed a complex analysis of melanoma epidemiology, by analyzing time trends in gender, age, anatomic site and morphology specific incidence rates between 1965 and 2009, in south and north regions of Norway. The main finding is that solar radiation may not have a negative role on certain types of melanoma, like for those on anatomic sites not directly exposed to the sun; moreover, the impact of sun exposure is different for various morphological types (nodular melanoma versus superficial-spreading melanoma), underlining the heterogeneity of melanoma. Our updated time trends show different course by age, gender and anatomic site. More importantly, following a period with rapid increase in melanoma incidence, we observed stable incidence rates after 1990s, and even decreasing rates for young population. However, there are subtle differences between north and south regions, in particular for the female population. For melanoma on shielded sites (like perianal skin and anorectal mucosa) trends continue to be stable during a long period of time. We found differences in the latitudinal gradient for melanoma incidence on different body sites with various sun exposure patterns. The latitudinal gradient was highest for trunk compared with head and neck, while no such latitudinal gradient was observed for melanomas on sites rarely (foot) or not exposed to the sun (anorectal and uveal melanomas). Our data stress that solar radiation is a risk factor for all anatomic sun-exposed sites, emphasizing the role of intermittent exposures, in particular for young individuals