Lung cancer mortality from exposure to chrysotile asbestos and smoking: a case-control study within a cohort in China

Our plain-English summary of Lung cancer mortality from exposure to chrysotile asbestos and smoking: a case-control study within a cohort in China, by E. Yano, X. Wang, M. Wang, et al (Occupational and Environmental Medicine, 2010).

The study

• Authors: E. Yano, X. Wang, M. Wang, H. Qiu, Z. Wang
• Journal: Occupational and Environmental Medicine
• Published: 2010;67(12):867-71
• Cited by: 31 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objective: To confirm the association between exposure to chrysotile asbestos and lung cancer risk and to demonstrate the combined effect of smoking and asbestos exposure.

Methods: A case-control study of 1139 asbestos workers identified 41 male lung cancer cases in 2001; each case was matched by age (±5 years) with five controls. Workers in seven workshops were categorised into high-, medium- and low-exposure subgroups, and conditional logistic regression was applied to estimate the odds ratios for lung cancer risk associated with the different exposure levels. Smoking, age at first exposure, and exposure duration were considered as covariates/confounding factors. A joint effect of asbestos exposure and smoking on lung cancer risk was analysed using a conditional logistical model.

Results: 54% of cases had high exposure and 24% low exposure, while 24% of controls had high exposure and 44% low exposure. Smoking was more common in cases (90%) than in controls (73%). The adjusted OR for lung cancer was 3.66 (95% CI 1.61 to 8.29) for high exposure and was elevated slightly for medium exposure (1.25; 95% CI 0.47 to 3.31). Smoking was related to lung cancer risk (OR 3.33; 95% CI 1.10 to 10.08). In comparison with the low-exposure non-smoking group, the OR for the high-exposure smoking group was 10.39 (1.34 to 82.45), in contrast to 5.23 (0.50 to 54.58) for high-exposure non-smoking workers.

Conclusions: These results confirm the strong association between exposure to chrysotile asbestos and lung cancer risk, and support an interactive effect of asbestos exposure and smoking which is more than additive.

In plain English

The authors ran a case-control study within a cohort of 1139 male workers at an asbestos textile plant in China, who were followed for lung cancer until 2001. According to plant records, only chrysotile was used at the plant. Each of 41 lung cancer deaths was matched by age with five controls (205 controls). Workers were grouped by job into high, medium and low exposure. Compared with low exposure, the odds ratio for lung cancer was 3.66 (95% CI 1.61 to 8.29) for high exposure. For medium exposure it was 1.25 (0.47 to 3.31), which was not statistically significant. Smoking was also linked to higher risk. Compared with low-exposure non-smokers, high-exposure smokers had an odds ratio of 10.39 (1.34 to 82.45) and high-exposure non-smokers 5.23 (0.50 to 54.58). A synergy index of 1.55 (0.43 to 5.67) pointed to a more-than-additive combined effect but was not statistically significant. The authors concluded that the results confirm a strong association between chrysotile and lung cancer. They noted the small number of cases, and that only about half had a pathological diagnosis.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Nested case-control study within a cohort (cases and controls drawn from the same cohort)
• Who was studied: An open cohort of 1139 male workers at an asbestos textile plant in China. They were recruited from January 1972 to November 1996 and followed until 2001. Forty-one lung cancer cases were identified from death certificates, and each was matched by age at death (within 5 years) with five controls, giving 41 cases and 205 controls.
• Exposure: Chrysotile asbestos. According to plant records, chrysotile was the only type used since 1939, for textiles, cement products, friction materials, rubber products and heat-resistant materials. Available samples showed less than 0.001% tremolite fibre. Workers were grouped by job: high exposure (raw material and textile sections), medium exposure (rubber section, maintenance, cleaning) and low exposure (cement section, administration). Smoking was classed as never or ever.
• Main results:
  • Of the cases, 54% had high exposure and 24% low exposure. Of the controls, 24% had high exposure and 44% low exposure.
  • Compared with the low-exposure group, the high-exposure group had an odds ratio for lung cancer of 3.66 (95% CI 1.61 to 8.29), which was statistically significant.
  • Compared with the low-exposure group, the medium-exposure group had an odds ratio of 1.25 (95% CI 0.47 to 3.31), which was not statistically significant.
  • Smoking was more common in cases (90%) than in controls (73%). In the multivariate model (Table 2), smoking had an odds ratio of 3.20 (95% CI 1.06 to 9.66).
  • No effect of age or exposure duration on lung cancer risk was observed.
  • Joint effect, compared with low-exposure non-smokers: high-exposure smokers had an odds ratio of 10.39 (1.34 to 82.45), and high-exposure non-smokers had 5.23 (0.50 to 54.58).
  • Joint effect, compared with low-exposure non-smokers: medium-exposure smokers had an odds ratio of about 4.3 and low-exposure smokers about 3.0. Neither was statistically significant. No case among non-smokers had medium exposure.
  • The synergy index was 1.55 (95% CI 0.43 to 5.67). The authors read this as a combined effect of high exposure and smoking greater than additive, but it did not reach statistical significance.
  • Asbestosis was diagnosed in 16 cases (39%) and 37 controls (19%).
• The authors' conclusion: The authors concluded that the results confirm a strong association between exposure to chrysotile asbestos and lung cancer risk. They also concluded that the results support an interactive effect of asbestos exposure and smoking that is more than additive.
• Limitations the authors state:
  • The number of cases was small, which gave wide confidence intervals, especially in the joint-effect subgroup analysis.
  • Only about half of the lung cancer cases had a pathological diagnosis. The rest were diagnosed on the basis of CT and clinical course.
  • Smoking was recorded only as yes or no, with no detail on how much people smoked.
  • The chrysotile samples analysed may not have represented the plant's historical use, and amphibole contamination may have varied in earlier raw materials.
  • Asbestosis may have been underestimated, because of poor-quality early x-rays and Chinese diagnostic criteria. For this reason it was left out of the multivariate analysis.
  • The reference group was itself exposed to asbestos. The authors suggest that risk estimates might have been larger against an unexposed reference group.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile, Lung cancer.

Medical terms in this study, explained in our Lexicon: Lung Cancer, Chrysotile, Case-Control Study, Asbestos Exposure, Odds Ratio, Confounding.

Related studies

• Analysis of mortality in chrysotile asbestos miners in China — L. Du, X. Wang, et al. (2012)
• Cause-specific mortality in a Chinese chrysotile textile worker cohort — X. Wang, S. Lin, et al. (2013)
• Cause-specific mortality in relation to chrysotile-asbestos exposure in a Chinese cohort — S. Lin, X. Wang, et al. (2012)
• Mortality in a Chinese chrysotile miner cohort — X. Wang, S. Lin, et al. (2012)
• A 37-year observation of mortality in Chinese chrysotile asbestos workers — X. Wang, E. Yano, et al. (2012)
• Follow-up study of chrysotile asbestos textile workers: cohort mortality and case-control analyses — J.M. Dement, D.P. Brown, et al. (1994)

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