Lung function predicts survival in a cohort of asbestos cement workers
From the earliest reports of lung disorders in asbestos workers, which date from the early 1900s, to our current time where asbestos has been conclusively shown to cause a number of terrible cancers and diseases—with the various forms of mesothelioma, such as pleural mesothelioma and peritoneal mesothelioma, probably the most feared of them—the mineral’s health effects are as terrible as they are common to those exposed to it. In light of these hazards, most industrialized nations have banned any use of the mineral, but some, such as the United States and Canada, have preferred strict regulations to an actual ban. However, even for those nations that actually have banned the use of asbestos, the extreme latency that is often associated with asbestos-related diseases means that people will continue to develop lung cancer and mesothelioma for years to come.
One of the great questions of asbestos-disease epidemiology is whether or not the underlying changes that lead to the development of these diseases can be identified earlier in an exposed person’s life, before any outward manifestations of the malignancies make themselves known. If these initial changes could be identified and subsequently tracked, then people at risk could possibly begin treatments to counteract, or at least to attempt to slow down, the progression of the biophysical changes whose endpoint is the worker’s premature death. To accomplish this, former asbestos workers would have to undergo regular screening procedures which would track the precise physiological changes being undergone, as well as quantify them to previously identified changes.
A study that completed such a process has recently been released by Austrian researchers, who analyzed many years of screening data among a cohort of former asbestos workers. Their findings definitely indicate the presence of quantifiable changes among the study’s population members.
Overview of the Study
In 1974 a number of workers from an Austrian asbestos cement factory agreed to take part in a long-term study investigating asbestos exposure. Information dating back to 1950 was captured for some of these individuals and new members were possibly added to the cohort until 1981, when the use of unprotected asbestos was banned in Austria. All these workers received regular checkups and their vital statuses were tracked as well. In 1989, additional screening procedures, including clinical examination, lung-function tests and chest x-rays, were made available to the workers. A total of 322 workers took part in these checkups and the study reports on 309 of them.
For each of the study members, a complete asbestos exposure history was available, as were the results of all checkups from 1989 to 2006. Information on each worker’s smoking history was incorporated into the overall analysis as well. The authors analyzed a number of individual factors for their effects on life expectancy and cause of death.
The workers reported on their individual work histories, including the type of work accomplished and the places in the factory in which the work took place. From this information, an analysis of the average asbestos concentrations found in the various locations was conducted and a table developed that grouped these exposures on a scale of 0 to 4, with 0 meaning very low exposure and 4 meaning very high exposure. This table was developed using an exposure scale of fibers/cm3 and was then combined with the number of time the worker spent in this location to determine a worker’s cumulative asbestos exposure, reported in “fiber years.” Chrysotile was the most common asbestos used and most workers were only ever exposed to it, although a subset of workers were exposed to amphibole asbestos fibers, of which, crocidolite was the major form.
The authors report that by the end of their study in 2006, 82 of the original 309 workers had died. Of these 82, 34 died from cancer, 30 from cardiovascular diseases, 6 from respiratory diseases and 10 from other reasons not quantified. Of the 34 cancers, 6 were from lung cancer, 7 were from pleural mesothelioma, 4 were gastric cancers, 9 were digestive cancers, and there were 8 other individual cancers.
The authors found that for those who died of lung cancer, even after controlling for smoking and pure amphibole exposure, cumulative fiber years of asbestos exposure was a significant predictor of lung cancer. This was in contrast to the workers who developed mesothelioma. For this group, fiber years alone was not predictive of pleural mesothelioma onset, but amphibole exposure was highly predictive, as was long latency from first exposure to asbestos. The authors conclude, as have a number of other studies, that any exposure to amphibole asbestos is always a high risk for the future development of pleural mesothelioma.
The authors were surprised to see that higher fiber year figures were significantly predictive of stomach and some digestive track cancers. The worker’s exposures were not implicated in the development of colon or rectal cancer, but the findings linking asbestos exposure to these other cancers are some of the first to clearly show this relationship, so the authors call for more research into this question.
In terms of overall cumulative exposures, workers exposed to asbestos in excess of 70 fiber years saw their life expectancy figure decrease by 25%. Although this was smaller than smoking, it still correlated as a negative prognostic factor.
One of the most significant set of findings was the correlation between reduced lung function and a reduction in life expectancy. Any of the lung function parameters which showed a reduction in an individual worker’s lung efficiency were predictive of a reduced life expectancy. In fact, the authors state that lung function tests were much more predictive of a reduced life expectancy than were x-rays, other clinical examinations or a simple exposure history analysis. This finding should be a clear indication that measurable reduction of lung function for asbestos workers is indicative of potentially serious future medical issues.
The authors conclude their paper by recommending regular screening examinations of former asbestos workers. They state that their findings clearly indicate that screening exams could identify precursor stages of serious illnesses, which could allow patients to start receiving treatments before they present with full-on malignancies. They also recommend that former asbestos workers who are currently smokers immediately stop smoking, as there is an immediate benefit to one’s life expectancy when one quits smoking. All in all, this study goes a long way in showing that even as asbestos workers are prone to the development of a number of difficult malignancies, screening procedures and early treatment for them could be helpful to their future lives.