Posted on: 8/15/2012
Mini Kapoor, Haynes and Boone
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Although exposure to asbestos fibers ("asbestos") has been repeatedly cited as the root cause of mesothelioma both in the scientific and the legal community, scientific researchers continue to discover and publish numerous other causes of the disease. This article is an update on research in the field of mesothelioma, specifically highlighting the expanding list of causes of the disease. Mesothelioma is a rare form of cancer that develops in the protective lining that covers many of the internal organs in the human body. Mesothelioma can develop in the pleura (lining around the lungs), peritoneum (lining of the abdominal cavity), pericardium (sac around the heart), and the sac around the testis (tunica vaginalis). The most common site for the development of the disease is the lining around the lungs. Mesothelioma has a long latency period, up to 40 years in some cases. To date, there is no effective cure for the disease, especially in its advanced stages. It has been known for some time that exposure to asbestos causes mesothelioma. Recent research, however, shows that asbestos exposure is not the only cause of mesothelioma. The following have been cited in literature as additional causes of mesothelioma.
Carbon Nanotubes. Carbon nanotubes are products of nanotechnology, widely used in the electronics, cosmetics, and medicine industry due to their useful physicochemical properties, including strength, conductivity and chemical stability. Due to the similarity in the shapes and sizes of carbon nanotube fibers and asbestos fibers, there have been concerns in the recent years as to the toxicity of carbon nanotubes to the human body. Experimental studies in animals have shown that carbon nanotubes can result in toxicity similar to that observed with asbestos exposure. For example, studies where carbon nanotubes were implanted in pleural or peritoneal cavity of mice, a similar or greater degree of inflammation and fibrosis was observed as compared to that produced by asbestos fibers.1, 2 Furthermore, the fact that similar genetic alterations have been observed in murine and human mesothelioma, suggests that human tissue is similarly affected by carbon nanotubes.3
Genetic Predisposition to Mesothelioma Due to Mutation in BAP1 Gene. Because only a small fraction of people exposed to asbestos develop mesothelioma, and a high incidence of mesothelioma has been observed in some families, in a study funded by the National Cancer Institute, scientists sought to determine if these families had altered genetic makeup that predisposed them to the disease. The study, published in 2011, showed that family members with mesothelioma had a mutation in a gene called BAP1. The study further showed that when individuals with the BAP1 mutation were exposed to asbestos, their risk of developing mesothelioma was markedly increased.4 Authors of the study opined that their research was the first of its kind "to demonstrate that individual genetic makeup c[ould] greatly influence susceptibility to mesothelioma."5
Radiation. Exposure to X-ray contrast medium Thorostat (thorium dioxide) has been shown to cause mesothelioma. Once injected into the body, Thorostat is retained by the human body and continues to decay emitting alpha radiation inside the body. Studies aimed at determining the effect of Thorostat on the human body have focused on comparing the risk of developing mesothelioma between the general population and patients undergoing radiographic procedure with and without Thorostat. Patients with exposure to Thorostat showed a significantly elevated risk for mesothelioma. Other sources of radiation that have been linked to mesothelioma include radiation therapy during treatment of cancer and chronic exposure to low levels of radiation at atomic energy plants.6
Simian Virus 40. About 32 million people in the US were accidently exposed to the Simian virus 40 (SV40 virus) when they were injected with polio vaccine contaminated with SV40. The contaminated batches were used for 8 years from 1955 to 1963. A rising incidence of mesothelioma was reported in the 1970s onwards. The fact that SV40 has been shown to cause mesothelioma in animals raises the possibility that SV40 played a role in the increased incidence of the disease in people injected with polio vaccine contaminated with the SV40 virus.7 Furthermore, extensive molecular and epidemiological studies have not ruled out the possibility that SV40 causes mesothelioma in people.7, 8
Although not all the above listed agents have been conclusively shown to cause mesothelioma in humans, these potential alternative causes of mesothelioma discussed in literature, surely make it harder to say today with certainty that a person is suffering from mesothelioma due to asbestos exposure.
This is especially important in litigation in "meso" cases, where plaintiffs claim asbestos exposure as the cause of mesothelioma. In light of the scientific literature citing other causes of mesothelioma, it may be worthwhile for both a plaintiff's and a defendant's counsel to probe these alternative causes of mesothelioma. For example, an attorney representing a party in a meso case may investigate whether the plaintiff's lifestyle is such that he is excessively exposed to products containing carbon nanotubes such as while working at a electronics manufacturing facility, or whether prior to developing mesothelioma, plaintiff had radiation treatment or whether plaintiff lived near or worked at an atomic energy plant, or whether the plaintiff received polio vaccine during the time period when the vaccine was known to be contaminated with SV40 virus. Answers to these inquiries could be beneficial to the plaintiff's attorney in anticipating some of the defenses that the opposing party may assert. On the defendant's side, answers to these questions could be helpful towards weakening the causation element of the plaintiff's case by producing evidence of plaintiff's exposure to agents other than asbestos that could have caused mesothelioma.
Mini Kapoor is an associate in the Litigation Practice Group in the Houston office of Haynes and Boone, LLP. Dr. Kapoor received her Ph.D. in Biochemistry & Molecular Biology from University of Kansas Medical Center, Kansas City, Kansas and her J.D. from the University of Houston Law Center, Houston, Texas. Prior to entering the field of law, Ms. Kapoor worked for many years in genetics and genomics at The University of Texas M.D. Anderson Cancer Center, where she conducted research under several national grants. She has published many articles in peer-reviewed scientific journals and has presented frequently at scientific meetings and conferences in the United States and Europe.
References
1. Marie-Claude F. Jaurand, Annie Renier and Julien Daubriac, Mesothelioma: Do Asbestos and Carbon Nanotubes Pose the Same Health Risk? 6 Particle and Fibre Toxicology 1 (2009).
2. C. A. Poland et al., Carbon Nanotubes Introduced Into the Abdominal Cavity of Mice Show Asbestos-Like Pathogenicity in a Pilot Study, 3 Nature Nanotechnology, 423 (2008).
3. Jean Didier et al., Syntenic Relationships Between Genomic Profiles of Fiber-Induced Murine and Malignant Mesothelioma, 178 Am. Journal of Pathology, 881 (2011).
4. Joseph R. Testa et al., Germline BAP1 Mutations Predispose to Malignant Mesothelioma, 43 Nature Genetics, 1022 (2011).
5. NIH-Funded Researchers Discover Genetic Link to Mesothelioma, http://www.nih.gov/news/health/aug2011/nci-28.htm (last visited May 20, 2012).
6. Bharat Jasani and Allen Gibbs, Mesothelioma Not Associated With Asbesots Exposure, 136 Archives Pathology Laboratory Medicine 262 (2012).
7. C. Cicala, F. Pompetti and M. Carbone. SV40 Induces Mesothelioma in Hamsters, 142 Am. J. Pathology, 1524 (1993).
8. H. Yang, Joseph R. Testa and Michele Carbone, Mesothelioma Epidemiology, Carcinogenesis and Pathogenesis, 9 Current Treatment Options Oncology, 147 (2008).