American Journal of Epidemiology Advance Access originally published online on December 5, 2006
American Journal of Epidemiology 2007 165(2):233-234; doi:10.1093/aje/kwk087
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LETTERS TO THE EDITOR |
RE: "OCCUPATIONAL RISK FACTORS FOR ESOPHAGEAL AND STOMACH CANCERS AMONG FEMALE TEXTILE WORKERS IN SHANGHAI, CHINA"
1 Envirosafe Training and Consultants, Pittsburgh, PA 15239
2 Department of Environmental Medicine and Public Health, University of Padova, 2-35128 Padova, Italy
(e-mail: johnhlange{at}worldnet.att.net)
A recent issue of the Journal included an excellent and interesting paper by Wernli et al. (1) supporting the concept that exposure to organic dust that contains endotoxin has beneficial effects against cancer. We would like to comment on the commonly suggested confounder associated with lower rates of cancer in workers exposed to organic dust—smoking—and expand on the mechanism by which endotoxin in dust may be responsible for the observed benefits as related to this exposure.
Historically, a few reports suggested that dust reduced the rate of lung cancer (2), although most investigators dismissed this finding and inferred that this was a methodological issue relating to lower smoking rates in exposed populations. However, studies by this research group (3–5) investigating Chinese cotton textile workers, as well as other investigations of textile (6, 7) and agricultural (8) workers, specifically dairy farmers (9, 10), now support the position that this effect of a lower-than-expected rate of cancer is not a result of differences in smoking rates between study and control populations. A 1973 study by Henderson and Enterline (11) collected data on the smoking rates of cotton textile workers and reported that the rates were slightly higher (51.9 percent) than those of the control population (51.2 percent). A recent evaluation of smoking rates of cotton textile workers (12) also suggests that the rate for this population is higher than or similar to that for controls and the general population.
This study (1), as have others (2, 9), suggests that the mechanism for the lower rates of cancer is a result of endotoxin, a lipopolysaccharide constituent of the Gram-negative bacterial cell wall. Previous investigations (13, 14) have shown that many occupational groups are exposed to high levels of airborne dust containing endotoxin. Wernli et al. (1) suggest that the endotoxin results in stimulation of the immune system, which causes macrophages to become antitumor/carcinogenic. We previously suggested a mechanism for this antitumor activity through the involvement of toll-like receptors and cytotoxic mediators, such as cytokines (e.g., tumor necrosis factor, interleukins) (9, 10, 15). In combination, these result in cellular activation of apoptosis pathways resulting in death of the cancer cell. It has been suggested that toll-like receptors 2 and 4 are involved, which activate the signaling pathway involving MyD88 and in turn result in the activation of TRAF6 (15). This action then signals one or more of the following: nuclear transcription factor kappa B, p38, and mitogen-activated protein kinases such as the c-Jun-NH–terminal protein kinase, which act on apoptosis (12, 15). It is even possible that other known cellular signaling systems, such as ERK, and others that are not known are involved.
It is suggested that the mechanism is similar for each organ system reported to benefit from exposure, including cells associated with the stomach and esophagus. We propose that other organ systems have similar effects in lowering cancer rates and that this process is occurring in other occupational groups (e.g., sewage workers) (16) besides cotton textile and agricultural workers.
Additional research on observed lower-than-expected rates of cancer is warranted. Traditional explanations of methodological causes (e.g., confounders) for lower rates can no longer be used to account for these observations.
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ACKNOWLEDGMENTS |
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Conflict of interest: none declared.
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NOTES |
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Editor's note: In accordance with Journal policy, Wernli et al. were asked whether they wanted to respond to this letter, but they chose not to do so.
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References |
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 TOP References |
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- Wernli KJ, Fitzgibbons ED, Ray RM, et al. (2006) Occupational risk factors for esophageal and stomach cancers among female textile workers in Shanghai, China. Am J Epidemiol 163:717–25.
[Abstract/Free Full Text] - Enterline PE, Sykora JL, Keleti G, et al. (1985) Endotoxin, cotton dust and cancer. Lancet 2:934–5.[Web of Science][Medline]
- Wernli KJ, Ray RM, Gao DL, et al. (2003) Cancer among women textile workers in Shanghai, China: overall incidence patterns, 1989 –1998. Am J Ind Med 44:595–9.[CrossRef][Web of Science][Medline]
- Chang CK, Astrakianakis G, Thomas DB, et al. (2006) Occupational exposures and risks of liver cancer among Shanghai female textile workers—a case-cohort study. Int J Epidemiol 35:361–9.
[Abstract/Free Full Text] - De Roos AJ, Ray RM, Gao DL, et al. (2005) Colorectal cancer incidence among female textile workers in Shanghai, China: a case-control analysis of occupational exposures. Cancer Causes Control 16:1177–88.[CrossRef][Web of Science][Medline]
- Fritschi L, Lakhani R, Nadon L. (2004) Cancer incidence in textile manufacturing workers in Australia. J Occup Hyg 46:493–6.
- Laakkonen A, Kyyronen P, Kauppinen T, et al. (2006) Occupational exposure to eight organic dusts and respiratory cancer. Occup Environ Med 63:726–33.
[Abstract/Free Full Text] - Lange JH, Mastrangelo G, Fedeli U, et al. (2003) Endotoxin exposure and lung cancer risk: a dose-response relationship hidden beneath mortality differential by kind of farming. Ann Agric Environ Med 10:229–32.[Web of Science][Medline]
- Mastrangelo G, Marzia V, Milan G, et al. (2004) An exposure-dependent reduction of lung cancer in dairy farmers. Indoor Built Environ 13:35–44.
- Mastrangelo G, Grange JM, Fadda E, et al. (2005) Lung cancer risk: effect of dairy farming and the consequence of removing that occupational exposure. Am J Epidemiol 161:1037–46.
[Abstract/Free Full Text] - Henderson V and Enterline PE. (1973) An unusual mortality experience in cotton textile workers. J Occup Med 15:717–19.[Medline]
- Lange JH. Reduced lung cancer in workers exposed to organic dust: epidemiological and experimental evidence. Curr Top Toxicol (in press).
- Lange JH. (2000) Reduced cancer rates in agricultural workers: a benefit of environmental and occupational endotoxin exposure. Med Hypotheses 55:383–5.[CrossRef][Web of Science][Medline]
- Viet SM, Buchan R, Stallones L. (2001) Acute respiratory effects and endotoxin exposure during wheat harvesting in northeastern Colorado. Appl Occup Environ Hyg 16:685–97.[Medline]
- Lange JH, Mastrangelo G, Fadda E, et al. (2005) Elevated lung cancer risk shortly after smoking cessation: is it due to reduction of endotoxin exposure? Med Hypotheses 65:534–41.[CrossRef][Web of Science][Medline]
- Lange JH, Mastrangelo G, Thomulka KW. (2003) Will sewage workers with endotoxin-related symptoms have benefit of reduced lung cancer? (Letter). Occup Environ Med 60:142–9.
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