Background Crocidolite is known to be the most carcinogenic form of asbestos for mesothelioma. This study aimed to assess if there was a difference between crocidolite and mixed asbestos fibre exposure for rates of lung cancer incidence and mortality after adjusting for smoking.

Methods Administrative datasets were used to identify lung cancer incidence and deaths in three Western Australian cohorts of people exposed to: crocidolite as miners and millers at Wittenoom; crocidolite as residents of Wittenoom; and mixed asbestos fibres occupationally. Multivariable Poisson regression models were used to compare the 5 year incidence and mortality rates between these cohorts after starting a health surveillance program. Explanatory variables included radiological evidence of asbestosis and cumulative asbestos exposures as determined through our Asbestos Job-Exposure Matrix (AsbJEM) after adjusting for smoking pack years, time since smoking cessation, age and sex.

Results The 5 year lung cancer incidence (n=176) and mortality (n=125) rates increased with radiological evidence of asbestosis (2.4-fold), increasing cumulative asbestos exposure and smoking pack-years. Compared with crocidolite miners and millers, Wittenoom ex-residents had the lowest rates (Incidence Rate Ratio (RR): 0.31, 95% CI: 0.15–0.67; and Mortality RR: 0.39 95% CI: 0.17–0.88). However, there were no significant differences identified between people occupationally exposed to mixed asbestos fibres (Incidence Rate Ratio (RR): 0.92, 95% CI: 0.61–1.39; and Mortality RR: 1.07 95% CI: 0.66–1.73) and Wittenoom workers.

Conclusion Mixed asbestos fibre exposure seems to be an equally potent cause of lung cancer as crocidolite after adjusting for smoking history.