Epidemiology of malignant melanoma: intermittent or total accumulated exposure to the sun?

In accordance with the sunlight hypothesis for its etiology, the incidence of malignant melanoma generally increases with increasing proximity to the equator. There are exceptions to this pattern, prominent among which is the tendency for incidence to increase with increasing distance from the equator beyond latitude 50 degrees north in Europe. This anomaly is probably explicable in terms of climatic factors, geographic variation in skin pigmentation, and the sun-seeking behavior of those in the north. The incidence of malignant melanoma is increasing at about 5% a year in most white populations, while there is no consistent tendency for it to increase in black populations. This difference suggests that the increase is due to increasing sun exposure. Evidence from recent case-control studies is consistent with both intermittent intense exposure and total accumulated exposure to the sun causing an increase in risk of malignant melanoma. Reconciliation of these two different patterns of effect of sun exposure may lie in more careful measurement of sun exposure and analysis of exposure specific to the site at which each melanoma is observed to occur.