Geographical, urban/rural and socioeconomic variations in nonmelanoma skin cancer incidence: a population-based study in Ireland

Abstract

Background: Nonmelanoma skin cancer (NMSC) is the most common cancer in white populations worldwide. International comparisons in incidence are limited because few registries collect comprehensive population-based data.

Objectives: We describe spatial, urban/rural and socioeconomic variations in NMSC incidence in Ireland, overall and for basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) separately. Methods NMSC cases (n=47 347) diagnosed during 1994-2003 were extracted from the National Cancer Registry. Each case was allocated to a small area (electoral district, ED) based on address at diagnosis. Standardized incidence ratios (SIRs) were calculated and smoothed using a Bayesian conditional autoregressive model. Associations between disease and census-derived area-based socioeconomic factors (unemployment, employment type, early school leavers, deprivation category, population density) were investigated using negative binomial regression.

Results: The spatial and socioeconomic distributions differed by subtype, suggesting aetiological differences. For BCC, areas of higher risk were concentrated around the main cities, with small patches on the south and west coast. Higher risks for SCC were seen in the north-east, on the south, mid and north-west coast. BCC risk in males and females, and SCC in males, was significantly higher in those living in the least deprived areas. Risk of BCC and SCC in females was higher in the most densely populated areas.

Conclusions: We observed striking geographical variation in NMSC incidence, which cannot be satisfactorily explained on the basis of known risk factors. Differences by deprivation category and population density may reflect better access to cancer surveillance or care, as well as differences in risk factor exposure.