Spatial epidemiology of lung-cancer mortality : geographical heterogeneity and risk-factors assessment

Abstract

Cancer is the leading cause of mortality in Andalucía (southern Spain) for both men and women, and lung cancer is the main cause of cancer mortality for men. Radon-gas exposure is the second most important cause of lung-cancer after tobacco-smoking, which also causes larynx cancer, and Chronic Obstructive Pulmonary Disease (COPD). Radon-gas is a radioactive decay element which originates from radium. Consequently, presence in the soil varies according to lithology (rock composition) which is a surrogate measure for potential radon-gas exposure. Lithology can explain some lung-cancer deaths, but not deaths due to either larynx cancer or COPD. A small-area analysis was implemented for the period 1986-1995. Fully-Bayesian regression analysis was used to assess the association between lithology and the spatial distribution of lung-cancer deaths (25,006 cases). Area-level deprivation, a surrogate measure for tobacco-smoking, was accounted for. The number of deaths due to larynx cancer (3,653 cases) and COPD (5,143 cases) were also modelled for comparison purposes. Computation was accomplished via Markov Chain Monte Carlo methods, using WinBUGS software. The spatial distribution of lung-cancer deaths (but neither larynx cancer, nor COPD) was positively associated with lithology, which is consistent with current epidemiological knowledge. These results remained after adjusting for area-level deprivation. The model used allows for separate estimation of risk due to both lithology (RR = 1.02; 95% Credible Interval (CI) = 1.015 – 1.031) and deprivation (RR = 1.04; 95% CI = 1.033 – 1.048). This lithology score overcomes the difficulties in obtaining actual radon-gas measurements, and can be further improved. The results go some way to explaining the regional variability in lung cancer mortality in Southern Spain.