Objectives To characterise the relationship between mesothelioma risk and asbestos lung burden inGreat Britain. To identify the asbestos lung burdens due to current or recent occupational and environmental asbestos exposures, and estimate consequent mesothelioma risks.
Methods Lung tissue and lifetime occupational histories were obtained from 136 mesotheliomas, 263 lung cancers and a random sample of 130 individuals from the British population obtained from those having surgery for pneumothorax. Asbestos lung burdens by fibre type were estimated by Transmission Electron Microscopy. Odds ratios for mesothelioma were estimated for asbestos lung burden categories by logistic regression using lung cancers as controls; mesothelioma risk was then modelled by adjusting for asbestos-related lung cancer risk among controls. Changes in mesothelioma risk arising from occupational and environmental exposures in the past and more recently were estimated from asbestos lung burdens of pneumothorax patients by period of birth.
Results A linear relationship between mesothelioma risk and lung burden was seen up to 0.5 million fibres per dry gram of lung (mfpg), and a burden of 0.1 mfpg was associated with a lifetime mesothelioma risk of 1.4%. Mean asbestos lung burdens for mesothelioma, lung cancer and pneumothorax cases born <1965 were positively correlated with the mesothelioma ORs for job categories from previous analyses, with highest burdens associated with construction jobs. Across all jobs, mean lung burdens were highest for mesothelioma (0.223 mfpg), followed by lung cancer (0.060), pneumothorax cases born <1965 (0.045) and finally pneumothorax cases born more recently (0.004).
Conclusions The average lifetime risk of mesothelioma in those born since 1965 is an order of magnitude lower than for those born in earlier decades. Lung burden analyses from a larger sample of pneumothorax patients born since 1965 are needed to more precisely identify recent exposure circumstances that contribute to their residual mesothelioma risk.