The effect of asbestosis on lung cancer risk beyond the dose related effect of asbestos alone

Aims: To determine if the presence of asbestosis is a prerequisite for lung cancer in subjects with known exposure to blue asbestos ( crocidolite). Methods: Former workers and residents of Wittenoom with known amounts of asbestos exposure ( duration, intensity, and time since first exposure), current chest x ray and smoking information, participating in a cancer prevention programme ( n = 1988) were studied. The first plain chest radiograph taken at the time of recruitment into the cancer prevention programme was examined for radiographic evidence of asbestosis according to the UICC ( ILO) classification. Cox proportional hazards modelling was used to relate asbestosis, asbestos exposure, and lung cancer. Results: Between 1990 and 2002 there were 58 cases of lung cancer. Thirty six per cent of cases had radiographic evidence of asbestosis compared to 12% of study participants. Smoking status was the strongest predictor of lung cancer, with current smokers ( OR = 26.5, 95% CI 3.5 to 198) having the greatest risk. Radiographic asbestosis ( OR = 1.94, 95% CI 1.09 to 3.46) and asbestos exposure ( OR = 1.21 per f/ml-year, 95% CI 1.02 to 1.42) were significantly associated with an increased risk of lung cancer. There was an increased risk of lung cancer with increasing exposure in those without asbestosis. Conclusion: In this cohort of former workers and residents of Wittenoom, asbestosis is not a mandatory precursor for asbestos related lung cancer. These findings support the hypothesis that it is the asbestos fibres per se that cause lung cancer, which can develop with or without the presence of asbestosis.