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Journal ofASTM International, Vol. 8, No. 1 Paper ID JAI102786 Available online at www.astm.org Michael J. McCoy, 1Matthew E2. Wolter, and Kim E. Anderson3 Mesothelioma in Drywall Finishing Workers ABSTRACT: In this manuscript, we evaluate the context in which workers were exposed to drywall joint compound based on the state-of-the-art of the construction industry during the post-World War II era through the 1970s and conduct a review of the scientific literature associated with the drywall trade and occupational exposure to airborne asbestos from drywall finishing work practices. Specifically, this manu script evaluates the epidemiologic literature describing the apparent lack of association of mesothelioma to asbestos fibers utilized in drywall finishing materials in workers who were potentially occupationally ex posed to short-fiber chrysotile asbestos contained in some drywall joint compound products during the post-World War II era through the early to mid-1970s. This manuscript also provides an understanding of the state-of-the-art in drywall joint compound manufacturing during this period. KEYWORDS: chrysotile, asbestos, mesothelioma, drywall joint compound, drywall tapers, short-fiber Introduction The health effects of occupational exposure to asbestos are well documented in the scientific literature. The significant sequelae of asbestos exposure include asbestosis, lung cancer, and pleural and peritoneal ma lignant mesothelioma. Between 2500 and 3000 new cases of malignant mesothelioma are diagnosed annually in the United States, with malignant mesothelioma responsible for 15 000-20 000 deaths annually worldwide [1,2]. Mossman and Gee [3] reported that over 80 % of these malignant mesothelioma cases were caused by occupational exposure to asbestos-containing materials (ACMs) in the workplace, and other researchers have reported that asbestos is the leading cause of mesothelioma in the United States and the western world [1]. According to Ismail-Khan et al., the worldwide incidence of mesothelioma is increasing and it is expected to peak in 2020 [4]. Recent research also suggests that these tumors may have also been related to the SV40 virus used in the manufacture of polio vaccines in the 1950s, therapeutic radiation and the genetic predisposition in the absence of asbestos exposure [2,5]. This may be reflected in the fact that 10-20 % of mesothelioma cases are not associated with known asbestos exposure [6]. It should also be noted that a recent review article by Price and Ware found that for mesothelioma cases estimated to be diagnosed in 2008, 42 % of those cases will have a "cause" other than asbestos exposure [7]. In fact, Price and Ware stated, "The number of background mesothelioma cases projected for 2008, slightly more than 1000 or 42 %, is notable and growing as a percentage of all cases" [7]. In addition, fluoroedenite, erionite, zeolite, and single-wall carbon nanotubes are all suspected agents of mesothelioma [6,8-11]. With a latency of 20-40 years from asbestos exposure, mesothelioma often impacts workers and spouses in their retirement, at least a minimum of 10 years, if not multiple decades after their exposure [12]. In this manuscript, we evaluate the context in which workers were exposed to drywall joint compound based on the state-of-the-art of the construction industry during the post-World War II era through the 1970s and conduct a review of the scientific literature associated with the drywall trade and occupational exposure to airborne asbestos from drywall finishing work practices. This manuscript provides a compre hensive review of the epidemiologic literature associated with drywall finishing workers who were poten tially occupationally exposed to short-fiber chrysotile asbestos contained in some drywall joint compound products during the post-World War II era through the early to mid-1970s. Specifically, this manuscript Manuscript received October 16, 2009; accepted for publication October 28, 2010; published online November 2010. 1 Environmental Health and Safety, GZA GeoEnvironmental, Inc., Waukesha, WI 53186. 2 Environmental Health and Safety, GZA GeoEnvironmental, Inc., Waukesha, WI 53186. 3 Senior Principal/Director of Toxicology, Environmental Health and Safety, GZA GeoEnvironmental, Inc., Waukesha, WI 53186 (Corresponding author), e-mail: kim.anderson@gza.com Copyright 2011 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. 2 JOURNAL OF ASTM INTERNATIONAL reviews the available epidemiologic literature and the apparent lack of association between drywall fin ishing work and the development of mesothelioma in drywall workers. This manuscript also provides an understanding of the state-of-the-art in drywall joint compound manufacturing during this time period and the manufacturer's lack of information and knowledge related to the potential adverse health effects of worker exposures to asbestos-containing joint compounds prior to the late 1970s. The Construction Industries' Work with Asbestos-Containing Building Materials For over 50 years, the construction industries' workforce had performed work practices that resulted in exposure to ACMs, including asbestos-containing building materials (ACBMs). ACBMs were often sup plied by pass-through suppliers to construction company contractors. These products included insulation, spray fireproofing, cements, roofing materials, gaskets, caulks, joint compounds, vinyl floor tile, mastics, pipes, plasters, and many other materials. Construction workers may have also utilized or been exposed to fire-resistant clothing, including gloves and blankets, during construction and may have been exposed to other ACBMs, including but not limited to firebricks, lagging, and insulation on heating systems and ductwork installed during construction. According to the U.S. Department of Labor, Occupational Safety and Health Administration (OSHA), "...an estimated 1.3 million employees in the construction and gen eral industry face significant asbestos exposure on the job. Heaviest exposures occur in the construction industry, particularly during the removal of asbestos during renovation or demolition" [13]. Drywall Installers and Tapers (Finishers) According to the U.S. Department of Labor, Bureau of Labor Statistics (BLS), the construction industry employed an average of 1.19 million people in the United States in 1945 [14]. In the U.S. post-World War II era, drywall installers and tapers (finishers) made up a small portion of the overall construction work force, many of which may have been exposed to asbestos while performing their work practices. According to the BLS, a drywall taper or finisher is defined as a worker in the North American Industry Classification System grouping 238310, Construction and Extraction Operations, Standard Occu pational Classification (SOC) subgroup 47-2082, which "seal(s) joints between plasterboard or other wallboard to prepare (the) wall surface for painting or papering" [14]. Logically, drywall tapers' work practices included the use of drywall joint compound, of which most, if not all, contained a small per centage of short-fiber Grade 7 chrysotile asbestos for a defined time period [14]. The BLS estimated that drywall installers, ceiling tile installers and drywall tapers, SOC 47-2080, which included drywall tapers (SOC 47-2082), totaled 160 590 workers in May 2008, which is the most recent data available from the BLS [14]. Occupational-specific data is not available from the BLS prior to 2003 to define the number of drywall finishers and tapers (SOC 47-2082) working in the United States in the post-World War II era. However, the BLS reported that of the 160 590 drywall installers employed in May 2008, ceiling tile installers and tapers in May 2008, --128 740 workers were employed and categorized as drywall and ceiling tile installers, and 31 850 were employed and categorized specifically as drywall tapers [14]. The total number of construction workers in 2008 was --7.215 million workers according to the BLS. Assuming the percentage of drywall tapers has remained as a consistent proportion of the total con struction industry from the post-World War II era to present, or --0.44 % of the total workers in the construction industry, --5236 drywall tapers would have been in the workforce in 1945. In 1970, there were --3.654 million workers employed in the construction industry, again with 0.44 % being drywall tapers, -- 16 077 workers would have been employed as drywall tapers in 1970. If these estimations are considered, then the number of workers coded as SOC 47-2082 would have increased by --10 841 em ployees from 1945 to 1970, with an increase of --15 773 drywall tapers between 1970 and May 2008. While this is clearly a retrospective estimation of the BLS data, these estimates provide an overview of the approximate number of workers in the United States performing drywall work as compared to the overall number of workers in the construction trades in the United States during the post-World War II era. The advent of gypsum wallboard (GWB) occurred in the mid-to late 1940s. The rapid demand for post-World War II homes necessitated the transition from the labor-intensive plaster finish work to the more rapid installation of GWB and subsequent finishing that utilized a variety of joint compounds and finishing compound. Eventually, by the late 1960s, the drywall installation and finishing trades were MCCOY ET AL. ON MESOTHELIOMA IN DRYWALL WORKERS 3 performed by the rough carpentry unions and construction trade groups, while plasterers worked more commonly with plasters, stuccos, and specialty finishes. Short-Fiber Chrysotile Asbestos Utilized in Drywall Joint Compound Due to its physical properties, including thermal stability and flexibility, short-fiber chrysotile serpentine mineral fibers were used as a component in hundreds if not thousands of building products. These shortfiber chrysotile fibers were also incorporated into selected manufacturers' drywall joint compound begin ning in the early 1950s to mid-1960s or later depending on the manufacturer [15]. Chrysotile asbestos is a hydrated magnesium silicate, which has unique chemical characteristics and structures such that it remains pliable and strong for many years (or decades). Due to chrysotile's high tensile strength and thermal resistance, chrysotile was utilized to stabilize, fireproof, and insulate a wide variety of construction products. Chrysotile was generally used more frequently than the other commercial asbestos fiber types in construction products, particularly after the 1960s [16]. Background on chrysotile mining and milling provides an understanding of the chrysotile asbestos content and mineralogy contained in drywall joint compound and its potential toxicological impact on drywall workers. Chrysotile asbestos of the serpentine crystalline structure was historically, and is cur rently, mined in Canada, mainly in the eastern townships of Quebec. Historically, asbestos was mined in Zimbabwe, Russia (Ural Mountains), China, Italy, Brazil, and United States (California and Vermont). In 1955, more than half of the chrysotile produced in the world came from Canada and Russia [17]. In the Quebec chrysotile mining district, the primary chrysotile mines extended from the southern town of Asbestos (Jeffrey Mine) in Black Lake, Thetford, and East Broughton to the northeastern operation of the Carey Canadian operations where the bulk of Canadian chrysotile fiber was produced [17]. For decades, the Carey Canadian operation supplied an extensive volume of chrysotile asbestos, which was imported into the United States for incorporation into construction products, including joint compounds. At one time, the amphibole tremolite was considered a contaminant in chrysotile ACBMs, including some joint compounds. The tremolite content, if any, varied widely across building products based on the source of origin of the chrysotile ore. Researchers have found that several sources of chrysotile used in joint compound did not contain tremolite. Specifically, Butler, Pooley and Gunter et al. independently found no detectable amphibole tremolite fibers in chrysotile asbestos mined in the Canadian Carey operations [18-20]. Williams-Jones et al. found similar results in the Jeffrey Pitt mine where selected chrysotile deposits are tremolite-free [21]. Mining occurred at Jeffrey Pitt outside of silica-rich intrusion bodies which differ from tremolitecontaining chrysotile deposits found in the Thetford, Bells, and other asbestos area mines [17,22]. Langer and Nolan reported that tremolite asbestos was present in chrysotile ore from the Bell Mine in Thetford, Quebec [17]. Other studies have revealed that tremolite contamination in Thetford was two to three times higher than that of tremolite found in chrysotile mined in and around the Asbestos, Quebec region [23]. Addison and Davies found a presence of tremolite in 28 of 81 samples, which were examined from the Quebec mining region, excluding the Carey Canadian and Jeffrey Pitt mines at an average concentration of 0.09 % tremolite for both mines [24]. In the United States, the majority of chrysotile mining occurred in California, although chrysotile was historically mined in Vermont as part of the southern extension of the Quebec deposits [25]. Bernstein et al. and Gibbs reported in 2005 that no tremolite was present in "Calidra" chrysotile mined from the Coalinga mine in New Idria, California [26,27]. Drywall joint compounds historically contained calcite, quartz (silica), talc, mica, gypsum, clays (attapulgite and kaolinite), polyvinyl alcohol, and perlite in addition to short-fiber chrysotile asbestos [27,28]. While tremolite is a naturally occurring constituent of some talc based on the mines' geographic origin, talc can be identified in both its asbestiform and non-asbestiform geologic habits. In addition, Rohl et al. identified some consumer products that contained small quantities of tremolite as a component of talc, ranging from 0.1 % to 10.3 % [29]. However, talc processing, including crushing and grinding, resulted in talc cleavage fragments with lower aspect ratios as compared to commercial amphiboles. Initial talc content and subsequent tremolite content in joint compound likely varied significantly between manu facturers' formulae. The resulting tremolite content in joint compounds, which in many brands of joint compound was below the level of detection, would have been determined by the mining origin of the talc, MCCOY ET AL. ON MESOTHELIOMA IN DRYWALL WORKERS 5 6 JOURNAL OF ASTM INTERNATIONAL bein et al.'s study revealed no mesothelioma in drywall workers due to the long latency of the disease and that their cohort had not yet reached that latency threshold for development of mesothelioma. However, it is important to note that short-fiber chrysotile was included by some companies in their products as early as the late 1950s, and, as reported by Stern et al., some plaster products contained asbestos prior to the advent of joint compound [38]. Robinson et al. evaluated occupation and industry codes on death certifi cates from 19 states to evaluate the mortality risk among men and women employed in construction occupations who died during 1984-1986 [35]. Malignant mesothelioma or any combinations of pleural or peritoneal carcinoma were not reported in this evaluation of 61 682 death certificates [35]. Wang et al. also found no mesothelioma deaths in a cohort of 29 554 male construction workers, including drywall workers in North Carolina who died between 1988 and 1994. Wang et al. confirmed the findings of previous investigators that increased mortality risk exists among construction workers [37]. A study by Lipscomb and Dement, which evaluated a cohort of 10 938 active union carpenters that had worked at least three months between 1989 and 1992, determined the odds ratios for lung diseases defined by ICD-9 codes [36]. This study also identified no cases of pleural neoplasms in this cohort of union carpenters, which included 1525 carpenters whose predominant type of carpentry work was classified as "drywall" workers. Stern et al.'s study of the Operative Plasterers' and Cement Masons' (OPCM) Association of the United States and Canada, which was comprised of 36 000 members including 12 960 plasterers, revealed four cases of mesothelioma in the overall cohort [38]. In Stern et al.'s report, plasterers were defined as "...generally responsible for all interior and exterior plastering of drywall, cement, stucco, and stone imitation as well as taping and pointing of all joints, nail holes and bruises on wallboard and drywall" [38]. It is important to note that plasterers in the OPCM union were involved with work activities that were not included in the BLS's description of a "drywall taper." Stern et al. noted that plasterers in the OPCM often installed structural fireproofing and other ACBM, which contained amphibole asbestos, in addition to short-fiber chrysotile, making evaluation of this occupational cohort challenging based on the variety of ACBMs, including amphiboles, to which they worked with and were exposed [38]. Beginning in the early 1960s, the drywall installation and finishing trades were performed by the rough carpentry unions and then by specific construction trade groups by the late 1960s, while plasterers worked more commonly with plasters, stuccos and specialty finishes during that time. In June 1997, the U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health (NIOSH) published a mortality study stratified by occupation, industry and cause of death in 24 reporting states from 1984 to 1988 [39]. The measure of association utilized in this study was the proportionate mortality ratio (PMR), which was age-adjusted for four race-sex groups, which included male, female, African-American, and Caucasian. All occupations were included, except for housewives or homemakers, with a total of 1 713 413 decedents in the study. There was a total of 3580 deaths in drywall workers, with no deaths reported in this cohort for pleural or peritoneal mesothelioma. NIOSH currently maintains the National Occupational Mortality Sur veillance System (NOMS) data of death certificate data with coded occupational and industry information, including 28 states that have participated from 1984 through 1998. When evaluating the NOMS database for white male drywall workers, coded as "Drywall Installers" under the U.S. Census Bureau occupation code 573, the database revealed 3173 total deaths occurring in drywall workers, with an undefined number, but less than three, of those deaths attributed to pleural or peritoneal mesothelioma. While this most recent NIOSH data is exclusively available by electronic media, it suggests similar results as the 1997 NIOSH occupational mortality study [40]. It is important to note that epidemiologic studies, based on death certificate analyses, may have inherent error by incorrectly reporting the decedent's occupation and under-reporting co-morbid diseases, which may be important when evaluating mortality in an occupational population. Studies of mortality using death certificates are important surveillance tools for identifying potentially hazardous occupations and industries. Wang et al. noted that the data may lack occupational exposure histories, as well as information on non-occupational risk factors, such as smoking and diet, which may be important in evaluating mortality rates from all diseases [37]. However, Wang et al.'s study confirmed previous findings of increased mortality risks among construction workers, revealed statistically significant work-related increases in the PMR for malignant neoplasm of the buccal cavity, pharynx, and lung, as well as pneu- MCCOY ET AL. ON MESOTHELIOMA IN DRYWALL WORKERS 7 moconiosis, transportation accidents, and accidental falls, yet did not indicate an increase in mesothelioma in drywall workers above that of all other workers [37], It is also important to consider that occupational coding at death may not reflect the patient's true long-term occupational exposure to ACBM, As noted by Stern et al., there is always the potential for underdiagnosis of mesothelioma due the fact that the International Classification for Disease (ICD) code for mesothelioma does not include all sites where mesothelioma can occur [38], While misdiagnosis may result in a feasible bias in these mortality studies, due to the low incidence of mesothelioma, clinical progression, and the histologically unique nature of mesothelioma, a "large undercount of mesothelioma deaths," as identified in Stern et al.'s study of plasterers who died from 1972 to 1996 is generally unsupported, In summary, the preceding epidemiologic studies utilizing death certificates revealed a lack of association between drywall workers and the development of malignant mesothelioma above that of the general population and workforce, Recently published research on asbestos-related disease, fiber type and dimension indicated that amphibole asbestos, not serpentine asbestos, is the causative agent of mesothelioma, In fact, Berman and Crump, in performing a meta-analysis of asbestos-related cases, including the mesothelioma risk, found that "for mesothelioma, the hypothesis that chrysotile and amphibole are equally potent was strongly rejected by every metric and the hypothesis that (pure) chrysotile is non-potent for mesothelioma was not rejected by any metric" [41], Numerous scientific studies have been conducted which show that the short-fiber chrysotile asbestos utilized in joint compounds, termed Grade 7 chrysotile, is neither a caus ative agent nor is it associated with pleural or peritoneal mesothelioma from the inhalation of this fibrous material [26,35,42-47], Short-fiber Grade 7 chrysotile, which was used in drywall joint compound, has also been studied for its biopersistence, or biologic half-life, in the lung, Bernstein et al, extensively published on their research on the biopersistence of chrysotile asbestos compared with that of amphibole tremolite [48], They found that clearance of these shorter chrysotile fibers was either similar to or faster than the clearance of insoluble nuisance dusts, Bernstein et al, also reported that fibers less than 5 pm in length are effectively no different from non-fibrous particles and are cleared with similar kinetics and mechanisms as particles [48], The World Health Organization (WHO) confirmed that chrysotile is more rapidly cleared form the lung than are amphiboles and reported that the fiber length is an important determinant of alveolar clearance of chrysotile fibers [49], WHO reported that evidence from animal studies confirmed that short-fibers (less the 5 pm long) are cleared more rapidly than long fibers (longer than 5 pm long) [49], The National Institute of Environmental Health Sciences, in its Annual Report on Carcinogens, 11th Edition, reported that "ninety-one percent of the chrysotile used in 2002 was categorized as Grade 7 asbestos (with fiber lengths less than 3 mm) followed by Grades 4, 5, 6 and 3" [50], The U,S, Environ mental Protection Agency technical support document assigned zero risk to fibers less than 5 pm in length and panelists concurred that fibers shorter than 5 pm in length and more likely 10 pm in length should be assigned "zero potency" [51], Hodgson and Darton also concurred that in humans, the short-fiber chrysotile utilized in drywall joint compound is cleared from the lung in months, which might have less biological effect than amphibole fibers, which are typically cleared in years [47], Pistolesi and Rusthoven reported that amphiboles appear to be more carcinogenic and mutagenic in animal models and tissue cultures than those that are curled and more pliable, such as chrysotile [52], Roggli et al,, in a clinicopathological correlation of 1445 pleural mesothelioma cases, reported that commercial amphiboles are responsible for most of the mesothelioma cases observed in the United States [53], These studies provided additional mechanistic and biologic plausibility to the epidemiologic data which suggests a lack of mesothelioma development in drywall finishing workers, Airborne Exposure to Short-Fiber Chrysotile During Drywall Finishing Activities While both toxicological and epidemiologic literature support that short-fiber chrysotile found in joint compound products is not causative of mesothelioma, the scientific literature described the fiber types and sizes observed during drywall finishing activities, Significant work has been performed to evaluate the airborne chrysotile fiber concentrations measured during typical drywall finishing work activities [54-56], In 2008, Brorby et al, characterized the distribution of primary size and bundles in historical joint system 10 JOURNAL OF ASTM INTERNATIONAL were no federal regulations which required any special requirements for the use of asbestos-containing products until late 1971. Generally, joint compound manufacturers learned that potential asbestos exposure existed that might be harmful in the early 1970s, before any questions had been raised regarding the evidence of disease from exposures to joint compounds. Studies by industry in 1973 indicated that airborne asbestos concentrations associated with the mixing and sanding of drywall joint and spackling compounds were generally within the OSHA PELs but could occasionally approach or exceed them [74]. Further monitoring, dust control measures, or respirators, as required by OSHA, were recommended [74,75]. The first case report in the medical literature of lung cancer and asbestosis in a drywall worker was reported by Fischbein et al. in 1978 [76]. Fischbein et al. published a study in 1979, demonstrating that selected, but unnamed, brands of drywall joint compounds contained asbestos, whose peak concentrations associated with their use could exceed the applicable OSHA PELs and that irregular radiographic opacities were seen in some drywall workers with several years of exposure [34]. To reiterate, in 1980, Verma and Middleton conducted the initial and only study to measure the airborne asbestos concentrations during the use of both dry powder and pre-mix drywall joint compound while defining the 8-h TWA exposure concentrations for each [59]. Prior to this study, other research had only presented peak and short-term air sampling results, not eight-hour TWAs [72,77-79]. Some joint compound manufacturers had begun developing asbestos-free joint compound before there were any published reports suggesting any potential health hazard with the use of asbestos-containing joint compounds and some placed warning labels on their joint compounds in 1972. It should be noted that on Jan. 12, 1972, OSHA proposed a revised asbestos standard that was promulgated in July 1976. This 1972 proposed standard required the initial warning labels for joint compound that contained asbestos that was distributed outside of the factories that manufactured the product. Following the January 1972 proposal, OSHA established an Advisory Committee on Asbestos Dust to make recommendations regarding a permanent asbestos standard and to receive oral and written comments from the public. Summary It should be noted that the scientific and epidemiological journals in which the few studies that were published regarding what were essentially new toxicological findings of asbestos prior to the early 1970s were scientific with limited distribution in medical and epidemiologic journals and, in general, obscure to most of those in the general population. Generally, joint compound manufacturers became aware in the late 1960s of potential health hazards of asbestos to persons exposed in mines, factories, and textile mills with products other than joint compound. For example, few individuals or companies had ready access to the British Journal of Industrial Medicine or the Annals of Occupational Hygiene. Obviously, the 1960s were long before the advent of the internet or any method to obtain these studies other than a company or individual conducting frequent library research. Further, in the United States, there were no federal safety and health regulations for individual facilities until the implementation of OSHA in 1971. However, there is no doubt that selected workers in the construction industry were exposed to asbestos and contracted asbestos-related diseases, including mesothelioma. Currently, research is on-going to define the cellular basis for causation of mesothelioma. Regardless, the scientific literature for drywall tapers is strongly suggestive in conferring the lack of a relationship to their work assignments, which may have used drywall accessory products that contained small concentra tions of chrysotile asbestos and the epidemiologic evidence of mesothelioma in drywall workers. While lung cancer and asbestosis have been well described in drywall worker cohorts, mesothelioma develop ment has not been definitely associated with drywall finishing work in the scientific literature. The current literature's lack of epidemiologic relationship between drywall finishing workers and mesothelioma may be in part due to the unique biopersistence, limited toxicity, fiber dimensions and structure and morphology of short-fiber chrysotile, which was historically used in some joint compound systems. Despite the limited number of workers in the epidemiologic studies reviewed in the manuscript, the available evidence shows that the majority of asbestos fibers in ACBMs contain chrysotile fibers of less than 5 pm in length. Toxicological data suggests that these asbestos fibers are less carcinogenic than amphibole fibers. There fore, in comparison to other occupationally exposed workers, drywall finishing workers have a reduced risk of developing mesothelioma. Future research, particularly in areas of genetic causation of mesothe- MCCOY ET AL. ON MESOTHELIOMA IN DRYWALL WORKERS 11 lioma, additional epidemiologic studies of drywall finishing worker cohorts, and advanced survey methods for historic joint compound exposure assessment, would contribute to the body of knowledge on this consistently fatal disease process. Acknowledgments Dr. Anderson and Mr. McCoy have served as expert witnesses for both plaintiffs and/or defendants in toxic tort litigation involving asbestos, organics, intoxicants, metals and microbial agents. This work was solely funded by GZA GeoEnvironmental, Inc. References [1] Yang, H., Testa, J. R., and Carbone, M., "Mesothelioma Epidemiology, Carcinogenesis, and Patho genesis," Current Treatment Options in Oncology, Vol. 9, No. 2-3, 2008, pp. 147-57. [2] Zervos, M. D., Bizekis, C., and Pass, H. I., "Malignant Mesothelioma 2008," Curr. Opin. Pulm Med., Vol. 14, No. 4, 2008, pp. 303-309. [3] Mossman, B. T. and Gee, J. B., "Asbestos-Related Diseases," N. Engl. J. Med., Vol. 320, No. 26, 1989, pp. 1721-1730. 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