21.2.1 Non-melanoma skin cancer

The risk of non-melanoma skin cancer (NMSC) was highest in two types of area—in and around the major urban centres in RoI (but not around Belfast and Derry in NI) and in a number of coastal areas in both RoI and NI. The aetiology of this cancer is better understood than that of most other cancers. Apart from some uncommon exposures—immunosuppressants, arsenic—NMSC in light-skinned people is caused by UV exposure (International Agency for Research on Cancer, 1992; Armstrong and Kricker, 2001). A survey of urban dwellers in RoI in 1991 showed that the great majority were light-skinned and at high risk of skin cancer from UV exposure (Gibson et al., 1997). No information is available on the geographical distribution of skin types within Ireland.

UV exposure may be recreational, including sunbed use (Karagas et al., 2002; Boyle et al., 2010), or occupational—the main occupations involved in the past being farming, fishing and building work. Gibson et al. (1997) found that 16% of their sample had used sunbeds. Higher recreational exposures have been reported among the more affluent in Ireland (Corcoran et al., 1996; Boyle et al., 2010). In a random sample of 2,200 people in NI, subjects with higher education attainment were more likely to report that having a suntan made them feel “healthier” or “more attractive”, and to have used sunbeds in the past. 20% of the sample had used sunbeds in 2008, down from 28% in 2000. A survey in 1993 of people taking “sun holidays” from Dublin airport, 11% of whom lived in NI, showed a predominance of professional and non-manual workers, with only 11% describing themselves as “manual workers”, compared to 31% in the general population in the 1991 census (Corcoran et al., 1996).

The distribution of men involved in farming, fishing and other agricultural work is likely to vary considerably across the island, and is a possible explanatory factor for geographical variation in NMSC risk. As NMSC development requires long UV exposure, we looked at the occupational distribution by county as given in the 1981 censuses, 20 years before the midpoint of the period covered by this report (Central Statistics Office, 1986; Northern Ireland Statistics and Research Agency, 1982). Table 21.1 shows the percentage of men reported as being involved in outdoor occupations (with the exception of the building trades, for which there was no separate category) in 1981 (Central Statistics Office, 1986; Northern Ireland Statistics and Research Agency, 1982). It is noticeable that the highest percentages in these occupations were in mostly inland counties of RoI, and the lowest in NI and there seems to be no relationship at county/district council level to the distribution of NMSC risk.

Ascertainment bias may account for part of the apparently higher NMSC risk in urban areas. NMSC is relatively asymptomatic and rarely fatal, which makes it likely that a significant number of cases escape medical attention. Rural populations are further from their GP (Teljeur et al., 2010) and are known to make less use of medical services, in RoI at least (Morrissey et al., 2008) and this may account for some of the difference. In Ireland as a whole, there was a clear correlation between higher NMSC risk and area measures of affluence such as higher educational attainment (both sexes) and higher employment (men). This relationship may be due to a greater use of medical services (both primary and secondary care in more educated and/or more prosperous populations. People with lower incomes are significantly less likely to be referred to a specialist (van Doorslaer et al., 2006; McBride et al., 2010).

The coastal pattern has no obvious explanation. Some of the areas of higher risk coincide with the location of fishing ports (Map 21.1) (Department of Agriculture and Rural Development, 2011; Department of Agriculture, Fisheries and Food, 2011) but the low numbers employed in fishing and the similarity of patterns between men and women make fishing an unlikely explanation. Migration of retired people to seaside areas also seems unlikely to have occurred at a rate which would explain the large differences in risk observed. Relatively few areas of high NMSC risk exist in areas of low sunshine (Map 21.2); however the relationship between higher sunshine levels and NMSC risk is not consistent. Areas in the south-east with high sunshine levels (by Irish standards) have low NMSC risk (Map 21.2). The higher risk in north and west Kerry and in Newry and Mourne is difficult to explain solely in terms of annual sunshine. Other factors related to coastal location may play a part. Areas around the coast may be less shaded from the sun and may also have features such as coastal walks, mountains etc. that draw residents out of their homes more, and for longer periods.

Map 21.1 Relative risk of non-melanoma skin cancer (both sexes) and location of larger fishing ports
relative risk of non-melanoma skin cancer (both sexes)	location of larger fishing ports
Map 21.2 Relative risk of non-melanoma skin cancer (both sexes ) and annual sunshine 1961-1990
relative risk of non-melanoma skin cancer (both sexes)	annual sunshine 1961-1990
Note: Sunshine data from Met Eireann http://www.met.ie/climate-ireland/sunshine.asp