FRIDAY, April 12 (HealthDay News) -- Smokers exposed to asbestos who also have the lung condition asbestosis have a significantly raised risk of developing lung cancer, according to a new study.
Quitting smoking after long-term asbestos exposure, however, can dramatically reduce the odds of developing this form of cancer, the researchers said.
"The interactions between asbestos exposure, asbestosis and smoking, and their influence on lung cancer risk are incompletely understood," study lead author Dr. Steven Markowitz, professor of occupational and environmental medicine at the School of Earth & Environmental Sciences at Queens College in New York City, said in a news release from the American Thoracic Society.
For the study, published online April 12 in the American Journal of Respiratory and Critical Care Medicine, researchers looked at medical records for more than 2,000 long-term asbestos workers and more than 54,000 blue-collar workers without asbestos exposure (the control group).
"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.
Nonsmokers with asbestos exposure had a death rate more than five times that of the people in the control group. When asbestos exposure was combined with smoking, the death rate from lung cancer was more than 28 times higher, the researchers found.
Asbestosis -- scarring of the lungs caused by inhalation of asbestos fibers -- compounds the problem, the researchers said. The study showed death rates from lung cancer were nearly 37 times higher among smokers exposed to asbestos who also had asbestosis.
But death rates from lung cancer dropped significantly among the asbestos workers who stopped smoking. In the decade after quitting, lung cancer mortality dropped from 177 deaths per 10,000 among smokers to 90 per 10,000 among former smokers, the study showed. Asbestos workers who stopped smoking for more than 30 years had lung cancer rates similar to asbestos insulators who never smoked, the researchers said.
"Our study provides strong evidence that asbestos exposure causes lung cancer through multiple mechanisms," Markowitz said. "Importantly, we also show that quitting smoking greatly reduces the increased lung cancer risk seen in this population."
The authors acknowledged that their findings were limited by the fact that the men's smoking status and asbestosis were assessed only once, and some of the men in the control group could have had some limited exposure to asbestos.
The U.S. Centers for Disease Control and Prevention provides more information on lung cancer risk factors.