Risk of Several Cancers is Higher in Urban Areas after Adjusting for Socioeconomic Status. Results from a Two-Country Population-Based Study of 18 Common Cancers

Some studies suggest that there are urban–rural variations in cancer incidence but whether these simply reflect urban–rural socioeconomic variation is unclear. We investigated whether there were urban–rural variations in the incidence of 18 cancers, after adjusting for socioeconomic status. Cancers diagnosed between 1995 and 2007 were extracted from the population-based National Cancer Registry Ireland and Northern Ireland Cancer Registry and categorised by urban–rural status, based on population density of area of residence at diagnosis (rural <1 person per hectare, intermediate 1–15 people per hectare, urban >15 people per hectare). Relative risks (RR) were calculated by negative binomial regression, adjusting for age, country and three area-based markers of socioeconomic status. Risks were significantly higher in both sexes in urban than rural residents with head and neck (males RR urban vs. rural = 1.53, 95 % CI 1.42–1.64; females RR = 1.29, 95 % CI 1.15–1.45), esophageal (males 1.21, 1.11–1.31; females 1.21, 1.08–1.35), stomach (males 1.36, 1.27–1.46; females 1.19, 1.08–1.30), colorectal (males 1.14, 1.09–1.18; females 1.04, 1.00–1.09), lung (males 1.54, 1.47–1.61; females 1.74, 1.65–1.84), non-melanoma skin (males 1.13, 1.10–1.17; females 1.23, 1.19–1.27) and bladder (males 1.30, 1.21–1.39; females 1.31, 1.17–1.46) cancers. Risks of breast, cervical, kidney and brain cancer were significantly higher in females in urban areas. Prostate cancer risk was higher in rural areas (0.94, 0.90–0.97). Other cancers showed no significant urban–rural differences. After adjusting for socioeconomic variation, urban–rural differences were evident for 12 of 18 cancers. Variations in healthcare utilization and known risk factors likely explain some of the observed associations. Explanations for others are unclear and, in the interests of equity, warrant further investigation