Search

Pigmented naevi (moles) are increasingly regarded as risk factors for the development of melanoma. The probability of melanoma developing from congenital naevi is proportional to the volume of the naevi. The risk of melanoma development from large naevi (diameter > 20 cm) is already present in the early years of childhood. The most important risk factor is the higher number of acquired naevi. This applies particularly to dysplastic (also called clinically atypical) naevi that not only represent the highest risk group but are also considered potential melanoma precursors. The development of acquired naevi (including dysplastic naevi) is dependant on the degree of skin pigmentation. The role of sunlight (ultraviolet radiation) in the development of melanoma is less significant than is generally assumed. The indirect effect of sunlight on melanoma development is to stimulate naevogenesis. One of the risk-modifying genes is the gene coding for melanocortin-1-receptor (MC1R). The presence of some gene variants has been found to lead to changes in melanin synthesis and is associated with a higher risk of melanoma. Recent research has shown that dysplastic naevi synthesise more phaeomelanin. There are also strong indications that dysplastic naevus cells suffer from chronic oxidative stress. This situation can lead to hypermutability and genetical instability.

The atypical naevus is both a risk factor for and a precursor lesion of melanoma. Sunlight is known to be an important aetiological factor for melanoma. Whether solar exposure is also involved in the initiation of (atypical) naevi is an issue of current interest. We performed a cross-sectional study among 270 inhabitants in the cloudy Netherlands and 282 white Dutch immigrants of the tropical island Curaçao to investigate whether solar exposure plays a role in the development of atypical naevi. All participants were interviewed and underwent total skin examination; banal melanocytic naevi and atypical naevi were counted. There was no significant difference in the mean number of melanocytic naevi > or = 2 mm or > or = 5 mm between Curaçao and the Netherlands. Furthermore, there was no significant difference in the mean crude and age standardized prevalence of atypical naevi between the Netherlands and Curaçao. In both groups individuals with atypical naevi had significantly more total naevi. Concerning the role of sun exposure in the development of naevi in the Netherlands, we found that the total naevus count had a significant association with cumulative sun exposure before the age of 12 as well as with two or more painful sunburns before the age of 12. In Curaçao these relationships were not observed. In contrast, however, on Curaçao the presence of atypical naevi showed an association (odds ratio = 2.6, 95% confidence interval 1.1-6.0) with the highest level of cumulative sun exposure and with painful sunburns before the age of 12 (odds ratio = 2.6, 95% confidence interval 1.2-5.5). In the Dutch group these associations were not significant. We hypothesize that in the development of banal naevi there is an association between the total number of naevi and sun exposure only at low exposure levels; however, after overstepping a critical threshold a further association between melanocytic naevi and sun exposure is lacking. Sunlight exposure before the age of 12 plays a complex role: only very high exposure levels seem to contribute to the development of atypical naevi.

A cross-sectional study was undertaken in 270 inhabitants of The Netherlands (moderate maritime climate, latitude 51 degrees 5' N-53 degrees 3' N) with skin types I-III and 757 inhabitants of the tropical island Curaçao (latitude 12 degrees 2' N-12 degrees 23' N). The latter group consisted of 282 White individuals (mostly Dutch immigrants) and 475 people with non-White skin types IV, V and VI. All participants underwent total skin examination and melanocytic naevi (MN) and clinically atypical naevi (AN) were noted. There was no statistical difference in the mean number of naevi > or = 2 mm or > or = 5 mm between the Curaçao and The Netherlands White groups, but the mean number of naevi > or = 2 mm and > or = 5 mm was significantly lower in the Curaçao non-White group. We found no obvious differences in mean naevus counts between genders and the various comparable age groups. Furthermore, we found no significant difference in mean crude and mean age-standardized prevalence of (one or more) AN between Whites in The Netherlands and on Curaçao. The Mantel-Haenszel prevalence ratio weighted for age and gender differences of Curaçao Whites vs non-Whites was 5.93 (95% confidence interval 3.9-12.0), demonstrating that AN are significantly less prevalent in darker skin types. In all groups, people with AN had significantly more MN than people without AN. We found a generation-dependent difference in the expression of AN among White inhabitants of The Netherlands and on Curaçao, with a higher prevalence of AN in the younger generation.

The precise role of ultraviolet radiation in the induction of nevocytic nevi is unsettled. We studied mole counts in relation to the attitude toward ultraviolet exposure in 508 students 18 to 30 years of age. Moles were counted on the chest, back, and legs. Lesions measuring 2 mm or less in diameter and those measuring more than 2 mm were recorded separately. Dysplastic nevi were also recorded separately. The attitude toward sun worship was related to the average periods of sunbathing, the frequency of holidays in sunny climates, and the use of artificial ultraviolet sources. The frequency of pigmented nevi showed no correlation with sun behavior, irrespective of sex, mole size, or burning and tanning propensities. This lack of correlation between ultraviolet exposure and mole counts held true for all solar parameters: periods of sunbathing, sunny holidays, and sunlamp usage. Contrary to expectation, there was a clear, although not statistically significant, excess of dysplastic nevi in subjects with short periods of ultraviolet exposure during leisure. From these data insufficient evidence emerges to support the hypothesis of a correlation between the occurrence of common nevocytic nevi and dysplastic nevi and the degree of insolation by natural or artificial ultraviolet radiation.