Sunlight as a risk factor of malignant melanoma of the skin

Abstract

The series of cutaneous melanoma compiled by the Finnish Cancer Registry, a total of 2501 cases covering all tumors diagnosed in Finland in 1953-1973, was analysed. The age adjusted incidence was equal in both sexes (about 3.5/105 in the 1970s). The risk more than doubled during the study period. The most common locations of melanoma in males were the trunk (48%) and lower limbs (17%), and in females the lower limbs (36%) and the trunk (28%).The age adjusted incidence rates were higher in urban areas than in rural districts and higher in southern parts of the country than in northern areas. However, after adjusting the rates for urban/rural residence of the population, the north south differences almost disappeared. In conclusion, the north south gradient was attributable to the degree of urbanization and not necessarily to the effect of latitude itself. Melanomas on the trunk in both sexes and those on the lower limbs in females had two features in common-the incidence of tumors on these locations increased markedly with time, and the age specific incidence rates increased sharply in middle age and levelled off thereafter. On the other hand, melanomas on the head and neck in both sexes and those on the lower limbs in males did not increase with time, and the risk was rather low in middle age and increased throughout life. The increase with time in the risk of melanoma could be accounted for by a cohort effect. These findings are not totally in accordance with the hypothesis of the association between sunlight and risk of melanoma, and it is concluded that recognition of sunlight as the only important risk factor of cutaneous melanoma may be an oversimplification of a complex problem.

Distribution of malignant melanoma on the body surface

“…This study of 37 population-based cancer registries has confirmed earlier reports (Lee & Yongehaiyudha, 1971;Magnus, 1973;Teppo et al, 1978) that about 75% of melanomas occur on the relatively unexposed sites of the limbs and body. The site distribution of malignant melanoma would appear, as Teppo et al have suggested, to be at variance with the supposed role of UV as the major aetiological factor.…”

“…The important point about these two sites is that the differences in exposure are not marked and the differences in incidence small. Similar sex differences have been reported previously in isolated studies (Lee & Yongehaiyudha, 1971;Magnus, 1973;Teppo et al, 1978). An important feature of the argument that the site distribution of melanoma does not accord with exposure is the comparison with the non-melanoma skin tumours.…”

“…The high frequency of melanoma on relatively unexposed sites has led to the suggestion that other factors may be involved in the aetiology of melanoma (Teppo et al, 1978). The present study is of the site distribution of malignant melanoma among 37 caucasian populations located throughout the world.…”

“…But several studies have reported that tumours occur with great frequency at other sites, particularly the leg among females and the trunk among males (Davis et al, 1966;Bodenham, 1968;Lee & Yongehaiyudha, 1971;Magnus, 1973;Teppo et al, 1978). This contrasts with the non-melanoma skin tumours, for which UV is also thought to be the major aetiological factor, but of which 70-90% occur on the head and neck (Haenszel, 1963;Urbach, 1969;.…”

Malignant melanoma: social status and outdoor work

“…THE INCIDENCE of malignant melanoma is rising rapidly (Elwood & Lee, 1975;Lee, 1976;Magnus, 1977;Teppo et al, 1978;Malec & Eklund, 1978;SoodalterToman et al, 1979) and, although prognosis is improving (End Results, 1976), this is not keeping pace, and the death rate is rising at about 3 % a year (Lee et al, 1979). The reason for these changes is unknown.…”