ABESTOS AND SMOKING: THE MAJOR CAUSES OF LUNG CANCER

The chances of developing lung cancer associated with asbestos
exposure, asbestosis and smoking are dramatically increased when these
three risk factors are combined, and quitting smoking significantly
reduces the risk of developinglung cancer after long-term asbestos
exposure, according to a new study.
"The interactions between asbestos exposure, asbestosis and smoking,
and their influence on lung cancer risk are incompletely
understood,"said lead author Steven B. Markowitz, MD DrPH, professor
of occupational and environmental medicine at the School of Earth &
Environmental Sciences at Queens College in New York."In our study of
a large cohortof asbestos-exposed insulators and more than 50,000
non-exposed controls, we found that each individualrisk 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 increasedthe risk of developing
lung cancer almost 37-fold."
The findings were published online ahead of print publication in the
American Thoracic Society's American Journal of Respiratory and
Critical Care Medicine.
The study included 2,377 long-term North American insulators and
54,243 male blue collar workers with no history of exposure to
asbestos from the Cancer Prevention Study II. Causes of death were
determined from the National Death Index.
Among non-smokers, asbestosexposure increased the rate ofdying from
lung cancer 5.2-fold, while the combination of smoking and asbestos
exposure increased the death rate more than 28-fold. Asbestosis
increased the risk of developing lung cancer among asbestos-exposed
subjects in both smokers and non-smokers, with the death rate from
lung cancer increasing 36.8-fold among asbestos-exposed smokers with
asbestosis.
Among insulators who quit smoking, lung cancer moralitydropped in the
10 years following smoking cessation from 177 deaths per 10,000 among
current smokers to 90 per 10,000 among those who quit. Lung cancer
rates amonginsulators who had stopped smoking more than 30 years
earlier were similar to those among insulators who had never smoked.
There were a few limitations to the study, including the factthat
smoking status and asbestosis were evaluated only once and that some
members of the control groupcould have been exposed to relatively
brief periods of asbestos.
"Our study provides strong evidence that asbestos exposure causes lung
cancer through multiple mechanisms," said Dr. Markowitz. "Importantly,
we also show that quitting smoking greatly reduces the increased lung
cancer risk seen in this population."