Relationship between Latitude and Melanoma in Italy

Objective. Evaluate the ecological relationship between skin melanoma epidemiology and latitude in Italy. Methods. We used data from the Italian network of cancer registries (Airtum). In a Poisson model, we evaluated the effect on incidence, mortality, and survival of latitude, adjusting for some demographic, social, phenotypic, and behavioural variables. Results. Incidence increased in Italy by 17% for each degree of increase in latitude. The effect of latitude was statistically significantly present also adjusting for other variables (incidence rate ratio = 1.08). The effect of latitude on increasing mortality (mortality rate ratio = 1.27) and improving survival (relative excess risk of death = 0.93) was no longer present in the multivariate model. Conclusion. Melanoma incidence, mortality, and survival vary in Italy according to latitude. After adjustment for several confounders, incidence still grows with growing latitude. Presumably, latitude expresses other variables that might be related to individual susceptibility and/or local care. 1. Introduction Although Italy is “the land where the lemon trees bloom,” as Goethe recited [1], the Italian climate changes dramatically from the cold Alpine regions in the North, to the subtropical areas in the South [2]. Italy stretches for about 1,000 kilometres from 47° to 35° latitude north, and the ultra violet (UV) irradiation varies accordingly with a north to south increasing trend [3]. Sun exposure is included among the major causes of skin melanoma (MM) [4] although its role is still controversial [5]. The UV affects skin causing genetic changes and immune function impairment; it also stimulates the production of growth factors and the formation of free radicals [6]. Phenotype traits significantly influenced the risk of melanoma [7]. The incidence of MM in white populations generally increases when latitude decreases, with the highest recorded incidence occurring in Australia, where the annual rates are 10–20 times the rates in Europe [8]. In New Zealand, MM incidence and mortality rates increased with increasing proximity to the equator in both sexes [9]. A Norwegian study described a latitude gradient for MM with decreasing incidence with increasing latitude [9, 10]; the same result was found in Sweden, for both general population [11] and children [12], and in Australia [13]. MM incidence increased at lower latitude [14] also among non-Hispanic whites in the USA. Studies in Spain [15], in Sweden [16], and in Australia and New Zeeland [17] document a link between latitude and MM mortality. In the USA,