[The sun and malignant melanoma]

Abstract

The aetiological role of sunlight in the development of cutaneous malignat melanoma (CMM) is still controversial. The aim of the present review is to discuss the contradictory findings and to reinterpret them in the light of recent epidemiological results. The following clinical and epidemiological features have raised doubts on an aetiological impact of sunlight in CMM development: the anatomical distribution of CMM does not closely match the body areas most exposed to sunlight, and CMM is most common during the middle decades of life (except for the subtype of lentigo maligna melanoma, which accounts for 10% of all CMM). Furthermore, no elevated CMM risk after sunburns or increased sun exposure has been detected in most of the case control studies performed so far. The most important risk factors, however, were the total number of melanocytic naevi in whole-body counts followed by such pigmentation characteristics as skin type and hair colour. On the other hand, the CMM incidence increases in white populations with increasing proximity of domicile to the equator and thus with increasing intensity of UV irradiation, and 5-10 times higher incidence rates have been reported from Australia and the southern states of the USA than from Europe. In industrialized nations with white populations a steep increase in CMM incidence has been described, with the main rise in body regions more frequently exposed to the sun in the last decades (trunk in men and boys and lower extremities in girls and women). Two results from recent epidemiological studies may help to clarify the contradictory findings above: first, sunburn in childhood and adolescence was shown in several case control studies to significantly elevate the risk of melanoma development, but further sunburn during adulthood did not contribute to any further risk elevation. Secondly, a study in Canadian school children revealed significantly higher naevus counts in subjects with numerous or severe episodes of sunburn in the previous 5 years. In conclusion, exposure to the sun in childhood and adolescence induces melanocytic naevi, which are known as markers of an elevated melanoma risk as well as possible precursors of CMM. Strategies to reduce melanoma incidence should therefore begin by restricting exposure to sunlight in young children and adolescents.