© The Author 2007. Published by Oxford University Press.
ARTICLES |
Lung Cancer Risk Among Female Textile Workers Exposed to Endotoxin
Affiliations of authors: Departments of Environmental and Occupational Health Sciences (GA, NSS, JEC, HC) and Epidemiology (KJW, DBT, HC), University of Washington, Seattle, WA; Fred Hutchinson Cancer Research Center, Program in Epidemiology, Seattle, WA (RR, ZF, WL, KJW, EDF, DBT); Zhong Shan Hospital Cancer Center, Shanghai, People's Republic of China (DLG)
Correspondence to: George Astrakianakis, PhD, Occupational Health and Safety Agency for Healthcare, 301-1195 West Broadway, Vancouver, BC, Canada (e-mail: george{at}ohsah.bc.ca).
Background: Reduced risk of lung cancer among workers in the cotton textile industry has been observed since the 1970s. Bacterial endotoxin, a contaminant of raw cotton fiber and cotton dust, has been proposed as a protective agent that may act through the innate and acquired immune systems. We examine the association between endotoxin exposure and lung cancer risk in a cohort of female textile workers.
Methods: We conducted a case–cohort study nested within a cohort of 267 400 female textile workers in Shanghai, China. We compared the cumulative exposure histories of 628 case patients diagnosed with incident lung cancer from January 1, 1989, through December 31, 1998, with those of a lung cancer–free reference subcohort of 3184 workers who were frequency matched by 5-year age-groups to all cancer patients in the cohort. Cumulative endotoxin exposure for all participants was based on historic measurements and on additional measurements for this study. Relative risks and 95% confidence intervals (CIs) were estimated by hazard ratios (HRs) from Cox proportional hazards models. We conducted exposure–response trend analyses by use of cumulative exposures with lag times of 0, 5, 10, 15, or 20 years to account for disease latency. All analyses controlled for age and smoking status. All statistical tests were two-sided.
Results: Cumulative exposure to endotoxin was strongly, statistically significantly, and inversely associated with lung cancer risk. The inverse trend was greatest with a 20-year lag time, for which highest endotoxin exposure was associated with a statistically significantly 40% less risk of lung cancer (HR = 0.60, 95% CI = 0.43 to 0.83; Ptrend across quintiles = .002) than nonexposure. From a reported population rate of lung cancer among women in Shanghai of 19.1 per 100 000 for the year 2000 and the estimated reduction in risk of lung cancer observed for 20 years of endotoxin exposure in this population of workers, the incidence of lung cancer in this cohort was reduced by approximately 7.6 per 100 000 (range = 3.2–10.9 per 100 000).
Conclusions: Long-term and high-level exposure to endotoxin, compared with no exposure, appears to be associated with a reduced risk of lung cancer in this cohort.
| CONTEXT AND CAVEATS Prior knowledge The risk of lung cancer appeared to be reduced among workers in the cotton textile industry. Study design Case–cohort study nested in a well-characterized prospective cohort of women in the cotton textile industry in Shanghai, China. Contribution Increased exposure to endotoxin was associated with a decreased risk of lung cancer among women in the Shanghai textile industry. The magnitude of the decreased risk increased with level of exposure and with increasing time of exposure. Implications Because the inverse association between endotoxin exposure and lung cancer risk became increasingly strong as recent exposures were discounted, the observed effect may be acting at an early stage during lung carcinogenesis. Limitations Potential sources of bias include the healthy worker effect (because sensitive workers may have transferred from high-exposure to low-exposure positions) and misclassification of exposure.
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Manuscript received August 13, 2006; revised December 13, 2006; accepted January 12, 2007.
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J Natl Cancer Inst 2007 99: 339.
J Natl Cancer Inst 2007 99: 337.
J Natl Cancer Inst 2007 99: 337.
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