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Combination of asbestos exposure, asbestosis, smoking amplified lung cancer risk
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Lung cancer risk associated with asbestos exposure, asbestosis and smoking was significantly increased when risk factors were combined, according to study results.
However, quitting smoking was found to considerably reduce the risk for developing lung cancer after long-term asbestos exposure.
Steven B. Markowitz, MD, DrPH, professor of occupational and environmental medicine at Queens College in New York, and colleagues conducted the study to assess the individual influence of asbestos exposure, asbestosis and smoking — as well as their relation to lung cancer risk — in an asbestos-exposed cohort.
The researchers examined long-term North American insulators (n= 2,377) and compared them with male blue-collar workers with no history of exposure to asbestos (n=54,243) who participated in the Cancer Prevention Study II.
Data from the insulator cohort consisted of age, duration of work and duration from onset of work as an insulator, smoking history, parenchymal asbestosis, asbestos-related pleural fibrosis and low FEV1/FVC (<65%).
Comparative data from the Cancer Prevention Study included smoking status (current, former or never); pack-years categories (0-9 through 80-89 pack-years); years since quitting for former smokers; and the number of lung cancer deaths from 1982 to 2008.
The researchers calculated death rates as the number of lung cancer deaths divided by the number of person-years for each group for any selected time period. Poisson regression modeling was used for all comparisons of the Cancer Prevention Study cohort to the insulator cohort. Cox proportional hazard modeling was used for all data within insulator cohort analyses.
According to study results, lung cancer was responsible for 339 (19%) insulator deaths. In particular, lung cancer mortality was increased by asbestos exposure among nonsmokers (rate ratio=3.6; 95% CI, 1.7-7.6), by asbestosis among nonsmokers (rate ratio=7.4; 95% CI, 4-13.7) and by smoking without asbestos exposure (rate ratio=10.3; 95% CI, 8.8-12.2).
“We found that each individual risk factor was associated with increased risk of developing lung cancer, while the combination of two risk factors further increased the risk and the combination of all three risk factors increased the risk of developing lung cancer almost 37-fold,” Markowitz said in a press release.
The dual effect of smoking and asbestos alone was additive (rate ratio=14.4; 95% CI, 10.7-19.4), and when combined with asbestosis, the effect was supra-additive (rate ratio=36.8; 95% CI, 30.1-46).
The researchers observed that insulator lung cancer mortality was reduced by half within 10 years of smoking cessation. Insulators who had stopped smoking more than 30 years earlier were found to have similar lung cancer rates as insulators who had never smoked.
“Asbestos exposure without associated asbestosis raises the relative risk of lung cancer among non-smokers and is additive to the risk of smoking,” Markowitz and colleagues wrote. “Asbestosis further increases the lung cancer risk and, considered jointly with smoking, has a supra-additive effect on lung cancer risk. This differential pattern of risk dependent upon the absence or presence of asbestosis continues with smoking cessation. The risk of lung cancer death among insulators who had quit smoking at least 30 years previously converges with that of never-smoking insulators.”
Disclosure: The researchers report no relevant financial disclosures.
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