21.2.8 Melanoma of the skin

As with non-melanoma skin cancer (NMSC), UV exposure causes melanoma of the skin (International Agency for Research on Cancer, 2001; Armstrong and Kricker, 2001). However, screening or case-finding may increase the number of early lesions detected and may confound the effects of sun exposure to some extent. As it is generally accepted that NMSC risk depends largely on lifetime exposure to UV radiation, while melanoma is related to recreational and intermittent exposure (International Agency for Research on Cancer, 2001; Armstrong and Kricker, 2001), it would be expected that their distribution patterns would differ somewhat.

Map 21.4 Relative risk of melanoma 1994-2007 and annual sunshine hours 1961-1990
Relative risk of melanoma (both sexes )Average hours of sunshine 1961-1990
Source: Sunshine data from Met Eireann http://www.met.ie/climate-ireland/sunshine.asp

As with NMSC, there was a higher risk in RoI than in NI; melanoma had a weaker relationship to population density and a stronger relationship to measures of affluence, than did NMSC. Because the number of cases was much lower for melanoma, small geographical variations in risk have been smoothed to a greater extent than for NMSC. Nevertheless, both similarities and differences can be seen. There was an area of high melanoma risk to the east of Belfast for both men and women which was not seen for NMSC, with a second area of higher risk around Craigavon. In NI, these areas are close to hospitals and may reflect case finding.

In RoI there was a clear band of higher risk running from south Wexford through Waterford to west Cork for both men and women, but the areas of higher risk observed for NMSC along the western seaboard were much less in evidence, especially for men. The pattern of risk in Dublin was similar to that for NMSC, with higher risk to the north and south of the city centre.

Despite the possible role of detection, ascertainment bias is unlikely to have played a major role in the geographical variations seen here and, as with NMSC, it is difficult to interpret the patterns either in terms of susceptibility, or of natural UV exposure at the place of residence. The socio-economic variation, and geographical variation in Belfast and Dublin, is almost certainly due to difference in holidaying practice two decades ago (Corcoran et al., 1996), but the higher risk along the south coast is more difficult to explain. However, there appears to be a stronger relationship with average sunshine levels than was seen for non-melanoma skin cancer (Map 21.4). A similar north-south gradient in melanoma risk has been reported in England (Quinn et al., 2005).

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