The most striking fact about the epidemiology of mesothelioma – and what has been known for decades – is that this form of cancer is most common in people that have experienced exposure to asbestos-containing environments, usually for an extended period of time. There has been an increase in the number of mesothelioma cases since the mid-20th Century. The cause of this escalation is thought to be widespread exposure to asbestos materials decades ago in many occupations.
“The incidence rates in industrialized countries range between 0.5 and three cases per million in men and between 0.2 and two cases per million in women.” according to a paper published by the Annals of Oncology.
There are approximately 2,500 new cases of mesothelioma diagnosed each year in the United States. The annual death rate from mesothelioma has increased in the last thirty years. Part of this increase in the reported rate may be due to better diagnostic techniques. In the past, cases of mesothelioma disease may have been misdiagnosed since it is difficult to distinguish between this condition and lung adenocarcinoma, the most common form of lung cancer.
Incidence-Related Data of Mesothelioma
The incidence of mesothelioma cases in the United States is four times more prevalent in males than females. This is probably because more males than females were employed in occupations where the possibility of asbestos exposure was greater. According to data from the Surveillance, Epidemiology, and End Results Program, there was an increase by as much as three times in the number of cases in the most common form of the disease, pleural mesothelioma, in the Caucasian male population during the period of 1973 through 1984 in the United States.
Data suggests that the chances of a mesothelioma diagnosis increases with age. The incidence of the disease is 10 times greater in male populations that are between the ages of 60 and 64 than in male populations that are between the ages of 30 and 34. This may be the result of the approximate 20 to 40 year latency period of the disease. A person may be exposed to harmful asbestos particles at a young age, but the disease may not be diagnosed until the person is older, since it takes time for mesothelioma to develop.
Geographical epidemiological studies show that deaths from pleural mesothelioma in the United States, in both males and females during the period of 1968 through 1978, were considerably higher in locations where asbestos-containing environments were prevalent, such as around manufacturing plants and shipyards.
Although the majority of mesothelioma cases occur among populations that have primarily worked in asbestos mines, shipyards, construction and other asbestos-related industries, some data suggest that family members that live with these populations may also be at risk for mesothelioma. It is suspected that workers may have inadvertently carried asbestos dust material from the workplace to their homes by means of clothing, hair, or work tools. This is called paraoccupational exposure to asbestos.
Connection between Asbestos Fiber Types and Mesothelioma Incidence
Inhaled fibers implicated include the amosite, chrysotile, or crocidolite forms of asbestos. Suspicions of a link between the crocidolite asbestos and higher risk of mesothelioma prompted further epidemiological studies into fibers types as they relate to mesothelioma incidences. According to A. Walker, M.D. of Harvard University, Boston in an article titled, The Epidemiology of Mesothelioma, “Exposure to crocidolite asbestos fibers is the most important known cause of mesothelioma, with important contributions from amosite, and other related mineral fibers in localized areas.”
Other data from studies in the 1980′s show that the risk of mesothelioma increased when asbestos-related products in mining and manufacturing involved the use of crocidolite or amosite, in comparison to the use of chrysotile. The fibers contained in amosite and crocidolite have a needle-like structure that allow them to easily remain in the body once they are inhaled and ultimately cause disease.
A lower incidence of mesothelioma is associated with chrysotile because its fibers are curly-like in structure making them more difficult to inhale. If they are inhaled, the body can eliminate them more easily than the needle-like asbestos fiber types from amosite and crocidolite that penetrate lung tissue making them difficult to remove. Overall, epidemiological studies regarding asbestos-related conditions conclude the following:
- Data shows that chrysotile poses less risk for development of asbestos-related conditions than amosite or crocidolite in occupational environments.
- Mesothelioma and lung cancer has developed from various types of asbestos fibers.
- Workers involved in mining occupations or those that take part in manufacturing of asbestos products have resulted in a much lower incidence of lung cancer than workers involved in textile-related occupation environments. (Relative risks have been lower in cases when chrysotile has been used compared to cases when amphibole has been used)
- Incidence of mesothelioma significantly increases in cases when individuals work in asbestos-related environments and smoke cigarettes.
- Lack of exact measurements in regards to exposure levels and fiber types further complicate epidemiological studies that try to differentiate risk levels posed by various asbestos particle types.
The Future of Mesothelioma Incidence
Mesothelioma incidence continues to slowly increase. People who were exposed to asbestos in their younger years are just now beginning to manifest symptoms of the disease due to the long latency period. Epidemiologists suspect that the disease has now hit its “peak period” and that there may be a decline in incidence over the next decade; although, it is not certain how long the “peak period” will last.
Data collected from the Surveillance, Epidemiology, and End Results Program has been used to predict the number of mesothelioma cases over the next several decades. Scientists predict that the number of mesothelioma cases among U.S. women may hit 500 annually. Additional calculations predict that male mesothelioma cases would be just over 2,000 cases annually in the early 21st Century and then decrease over the next several decades to 500 cases annually.
Increased research and awareness regarding the dangers of inhaling the harmful fibers has grown and limits have been set for asbestos use and exposure levels to reduce mesothelioma incidence in the future.
Related: Women and mesothelioma.
Sources of information on this page: National Cancer Institute National Libraries of Medicine, Seattle Community Network, American College of Chest Physicians, European Respiratory Journal