Seasonal variation in the occurrence of cutaneous melanoma in Europe: influence of latitude. An analysis using the EUROCARE group of registries

The aim of our study was to analyse seasonal variations in melanoma incidence in Europe. Data from 28 117 cutaneous melanoma cases reported during 1978-1993 to the EUROCARE group of registries were analysed. There is a clear summer peak in incidence in Western countries (summer-winter ratio: 1.31 P < 0.0001; Nam's test), which was not observed in Central Europe (ratio: 1.06; P = 0.0699). The amplitude of seasonality is higher for females (ratio = 1.38, 95% Confidence Interval (CI) [1.31-1.44]) than for males (ratio = 1.21 95%CI [1.14-1.29]). It is also higher for upper and lower limbs (1.44 and 1.46, respectively), than for head and neck or trunk regions (1.09 and 1.20, respectively). The amplitude of seasonality also varies with latitude and increases with time: in a linear regression adjusting for age, gender and anatomical localisation, the date of diagnosis was significantly closer to summer solstice with decreasing latitude (P = 0.0005) and for more recent year of diagnosis (P = 0.0123). The effect of latitude on the amplitude of the seasonal variation in melanoma incidence in Europe may be an indicator of ultraviolet B (UVB) exposure. Furthermore, an increase in intentional sun exposure could lead to an increase in melanoma promotion and thus to an increase in the amplitude of seasonal variation.