Mesothelioma has one of the longest latency periods of any disease. It is not unusual for patients to develop the asbestos cancer many decades after their last exposure to asbestos. Now, a new German study offers a more detailed explanation of why that is.
Although the body is adept at ridding itself of many kinds of toxins, when asbestos fibers are inhaled or swallowed, their shape and size allow them to stay in the tissue indefinitely, causing inflammation that can eventually trigger malignant mesothelioma.
The new study, published in the European Respiratory Journal, is the first to study to level of asbestos fibers in the tissue of several individuals over time. It proves that, contrary to some theories, the fiber burden does not tend to decrease with time, no matter what kind of asbestos fiber is involved.
Asbestos Fibers and Mesothelioma
The study utilized data from the German Mesothelioma Register to identify patients who were suspected of having pleural mesothelioma or another asbestos-related disease and whose biopsies showed at least 500 fibers of asbestos per gram of lung tissue. To be included, individuals had to have been biopsied twice at minimum intervals of 4 years.
The team found datasets on 12 patients who had had biopsies at a median of 8-year intervals, with the longest interval being 21 years. In some cases, those biopsies were done during mesothelioma surgery, in others, they were completed as part of an autopsy.
They key finding is that, whether it had been three years (the minimum of the patients tested) or 29 years (the maximum) since a person’s last asbestos exposure, the number of asbestos fibers in the lungs remained constant.
“Pulmonary asbestos fibre burden was stable between both examinations,” writes lead author Inke Sabine Feder, a pathologist at Ruhr-University Bochum in Bochum, Germany. “This study is the first to present longitudinal intra-individual data about the asbestos fibre burden in living human lungs.”
Chrysotile as “Sticky” as Other Asbestos Types
Asbestos, the leading cause of malignant mesothelioma, comes in several sizes and shapes, including curly (serpentine) or straight. Chrysotile, which accounts for 90 percent of commercially-used asbestos, is a serpentine-shaped fiber while crocidolite, amosite, tremolite, and some others are amphiboles that are straight and sharp.
Some previous studies have suggested that the shape of chrysotile fibers makes it easier for the body to rid itself of them. But when they examined lung tissue samples with an electron microscope, the German team found mainly amphibole fibers in a third of the samples and mainly chrysotile fibers in the remaining two thirds.
The authors conclude, “Overall, this study very clearly demonstrates high biopersistence of not only amphibole but also chrysotile asbestos in the human lung and thus gives mechanistic explanations for the toxicity of the fibre and the long latency period of asbestos related diseases.”
Feder, IS, et al, “The asbestos fibre burden in human lungs: new insights into the chrysotile debate”, June 29, 2017, European Respiratory Journal