21. Discussion

This atlas demonstrates, for the island of Ireland, many of the patterns already seen in the cancer atlas of the Republic of Ireland (Carsin et al. 2009), but the inclusion of Northern Ireland allows some geographical trends to be seen more clearly. The juxtaposition of two similar populations with different health services is also of interest. Recorded variation in cancer rates across geographical areas may be attributed to three factors—true geographical variation in the underlying risk of cancer, differences in case ascertainment and definition, and random variation. The hypothesis suggested in this atlas is that the geographical variation is largely due to variation in cancer risk.

Geographical patterns

The mapping presented in this atlas shows a wide diversity of geographical patterns of risk, many of which are difficult to interpret. Mapping demonstrated broadly similar geographical patterns for men and women for most cancers. Three cancers (pancreas, brain and other central nervous system, and leukaemia) had an increasing gradient of risk from north-east to south-west, but apart from this there was no consistent gradient of risk across the island. There was a marked geographical variation in the risk of some common cancers—melanoma and non-melanoma skin, lung, prostate, oesophagus, stomach and gynaecological cancers—but very little for others—breast, colorectal and non-Hodgkin’s lymphoma.

Socio-economic and demographic variation

Overall, the relationships between socio-economic variables and cancer risk were similar for men and women. The strength of the relationship, and consequently the statistical significance, varied, but we did not observe any situation in which the effects of socio-economic factors were in opposite directions for men and women. Patterns consistent with known socio-economic gradients in cancer risk (Faggiano et al., 1997) were observed. Cancers of lung, stomach and head and neck in both sexes, colorectal, bladder and pancreas cancer in men and cervical cancer in women were all more common in areas of higher unemployment. Areas where a smaller proportion of the population had third-level qualifications had a higher risk of lung cancer (particularly in women) and stomach cancer in both sexes, and of cervical cancer and pancreatic cancer in women. Conversely, where unemployment was lower and/or educational levels higher, prostate and female breast cancer, as well as melanoma and non-melanoma skin cancer, were more common.

Most cancers were more frequent in urban areas (as measured by population density), after adjusting for the effect of age. This relationship was statistically significant for non-melanoma skin, colorectal, lung, stomach, bladder, head and neck and oesophageal cancer in both sexes and for breast, cervical, kidney and brain and other CNS cancer in women; a reciprocal relationship was seen only for prostate cancer.

We have previously noted a consistent, if weak, relationship between cancer and the percentage of people aged 65 and older living alone in RoI (Carsin et al., 2009). For this report, the cut-off point was set at 75 years and older, for compatibility between census measures in the two countries, and the relationship was not as consistently observed. However, a positive relationship was observed between increased cancer risk and an increased percentage of persons aged 75 and older living alone for non-melanoma skin, lung, breast, colorectal, stomach, pancreas, bladder, head and neck and oesophageal cancer and for leukaemia, for one or both sexes. This relationship was independent of the measures of deprivation used here, but may be a marker of area-based types of “deprivation”, such as poor diet and chronic ill-health, not identified by the conventional indices (Harrington et al., 2011; Layte et al., 2011). However, it may also be a marker of individual risk. In RoI in 2006, 46% of the population aged 75 and older was widowed and 19% unmarried, so most of those aged 75 and older and living alone are also likely to have been widowed (Central Statistics Office, 2007). Premature bereavement may be an indicator of a shared higher risk lifestyle. 

Building 6800
Cork Airport Business Park
Kinsale Road, Cork T12 CDF7
Email Contact us here
Tel: +353 (0) 21 4318014
Fax: +353 (0) 21 4318016

NCRI directions

Go to top