Occupational risk factors for mortality from stomach and lung cancer among rubber workers: an analysis using internal controls and refined exposure assessment

Our plain-English summary of Occupational risk factors for mortality from stomach and lung cancer among rubber workers: an analysis using internal controls and refined exposure assessment, by K. Straif, L. Chambless, S.K. Weiland, et al (International Journal of Epidemiology, 1999).

The study

• Authors: K. Straif, L. Chambless, S.K. Weiland, A. Wienke, M. Bungers, D. Taeger, U. Keil
• Journal: International Journal of Epidemiology
• Published: 1999;28(6):1037-43
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: To determine occupational risk factors for stomach and lung cancer among workers in the German rubber industry.

Methods: A cohort of all male German rubber workers (n = 11,633) who had been employed for at least one year in one of five study plants and who were alive and actively employed or retired on 1 January 1981 was followed for mortality from 1 January 1981 through December 1991. A subcohort of n = 8,933 workers who were hired after 1 January 1950 was defined to focus on working conditions in the more recent rubber industry. Work histories were reconstructed using routinely documented 'cost centre codes' and classified into six work areas as well as subgroups of some work areas. The work areas are: 1. preparation of materials, 2. production of technical rubber goods, 3. production of tyres, 4. storage and dispatch, 5. maintenance, 6. others. Standardized mortality ratios (SMR) and Cox proportional hazards models were calculated for each of the work areas (>1 year of employment in the respective work area). Hazard rate ratios were adjusted for age (time marker) and stratified for year of hire (1950-1959, > or =1960) and years of employment in the respective work area (1-9 years, > or =10 years); years of employment were lagged 10 years to account for latency.

Results: Compared to the national reference population mortality from cancer of stomach (observed 44, SMR = 117; 95% CI: 85-157) and lung (observed 154, SMR = 123; 95% CI: 104-144) was slightly increased. Using internal controls we observed excess deaths from stomach cancer in work area 1 (relative risk [RR] = 2.3; 95% CI: 1.2-4.2) and from lung cancer in work areas 1 (RR = 1.7; 95% CI: 1.2-2.3), 2 (RR = 1.5; 95% CI: 1.1-2.1), and 3 (RR = 1.3; 95% CI: 0.9-1.8). On the basis of cumulative years of employment an exposure response relationship was observed for mortality from both cancer sites among a subcategory of work area 1: weighing and mixing. Increased risks were also seen for lung cancer among workers employed in production of technical rubber goods.

Conclusion: Our results support an association between an excess mortality from stomach and lung cancer and employment in early production stages of rubber manufacturing, especially weighing and mixing. This may point to an aetiologic role of asbestos or carbon black. For stomach cancer additional risk factors, e.g. exposure to dust and talc, deserve further investigation. The results of the present study do not support a causal role of nitrosamines for stomach or lung cancer.

In plain English

This cohort study followed 8933 male blue-collar workers hired after 1 January 1950 at five German rubber plants, recording deaths in 1981–1991. Work areas came from company accounting codes; asbestos and other substances were not measured. Compared with West German men, stomach cancer deaths (44, SMR 117; 95% CI 85–157) and lung cancer deaths (154, SMR 123; 95% CI 104–144) were slightly increased. Men with more than a year in materials preparation were compared with all other cohort members, including men with less time there. They had relative risks of 2.3 (95% CI 1.2–4.2) for stomach cancer and 1.7 (1.2–2.3) for lung cancer. In weighing and mixing, the longest-employment group (described as more than 10 years) had a stomach cancer HRR of 4.0 (1.9–8.3). Men with more than a year in technical rubber goods, compared the same way, had a lung cancer relative risk of 1.5 (1.1–2.1). For stomach cancer, the authors concluded this may point to dust, possibly talc, asbestos or carbon black, and that a causal role of nitrosamines was not corroborated. For lung cancer, they speculated about asbestos, asbestos-contaminated talc and carbon black, and called nitrosamines' role equivocal.

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: Cohort study of mortality. It compared the cohort with the national population (standardized mortality ratios) and compared workers within the cohort with each other (internal controls, Cox proportional hazards models).
• Who was studied: The original cohort was all male German blue-collar workers of five study plants who were alive and actively employed or retired on 1 January 1981 (n = 11 633). The analysis was restricted to the 8933 workers hired after 1 January 1950 (1521 deaths), followed from 1 January 1981 to 31 December 1991.
• Exposure: Employment in rubber-industry work areas, reconstructed from company cost centre codes: 1. preparation of materials (1a. weighing and mixing; 1b. milling and calendering), 2. technical rubber goods, 3. tyres (3a. vulcanization; 3b. tubes), 4. storage and dispatch, 5. maintenance, 6. others. The authors describe weighing and mixing as the area with the heaviest exposure to dusts including carbon black, talc and asbestos. No fiber types or doses were measured.
• Main results:
  • Compared with the West German male reference population, the whole cohort had a slight increase in deaths from stomach cancer (44 deaths, SMR 117; 95% CI 85–157) and lung cancer (154 deaths, SMR 123; 95% CI 104–144).
  • Stomach cancer: the only statistically significant increase was in work area 1, preparation of materials. Men with more than a year in that area were compared with all other workers in the cohort, including those with less than a year there (17 deaths; relative risk 2.3; 95% CI 1.2–4.2).
  • Stomach cancer: the highest hazard rate ratio was among workers in the longest-employment group in weighing and mixing, described in the text as more than 10 years (10 deaths, HRR 4.0, 95% CI 1.9–8.3).
  • Lung cancer: among men with more than a year in the respective work area, each compared with all other workers, the relative risks were 1.7 (95% CI 1.2–2.3) in work area 1 (preparation of materials), 1.5 (1.1–2.1) in work area 2 (technical rubber goods), and 1.3 (0.9–1.8, not statistically significant) in work area 3 (tyres).
  • Lung cancer: risks were statistically significantly increased in all strata of weighing and mixing, for example HRR 1.9 (95% CI 1.2–3.1) in the longest-employment group.
  • Lung cancer: the authors stated that the pattern of risks did not support a causal association with employment in tyre production.
  • Lung cancer: the authors speculated, based on how exposures were distributed across work areas, that asbestos, asbestos-contaminated talc and carbon black may be risk factors.
  • Lung cancer: the authors described the role of nitrosamines as equivocal.
• The authors' conclusion: For stomach cancer, the authors concluded that their results and the literature support an association between weighing and mixing and increased risk. They said this may point to dust, possibly talc, asbestos or carbon black, and that a causal role of nitrosamines was not corroborated. For lung cancer, they speculated that asbestos, asbestos-contaminated talc and carbon black may be risk factors, and called the role of nitrosamines equivocal.
• Limitations the authors state:
  • Exposure was classified by work area rather than by specific substances. The authors say future studies need exposure information for specific carcinogens.
  • Production of technical rubber goods could not be divided into consistent subgroups across plants.

Topics

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

Medical terms in this study, explained in our Lexicon: Lung Cancer, standardized mortality ratio (SMR), rate ratio, Latency, Stomach Cancer, Relative Risk, Talc.

Related studies

• Exposure to nitrosamines, carbon black, asbestos, and talc and mortality from stomach, lung, and laryngeal cancer in a cohort of rubber workers — K. Straif, U. Keil, et al. (2000)
• Workplace risk factors for cancer in the German rubber industry: Part 1. Mortality from respiratory cancers — S.K. Weiland, K. Straif, et al. (1998)
• Occupational exposures and risk of stomach cancer by histological type — M. Santibañez, J. Alguacil, et al. (2012)
• Environmental and ecological factors of stomach cancer incidence and mortality: a systematic review study on ecological studies — S. Khazaei, A. Mohammadbeigi, et al. (2020)
• Talc-coated rice as a risk factor for stomach cancer — G.N. Stemmermann, L.N. Kolonel (1978)
• A survey of occupational cancer in the rubber and cablemaking industries: results of five-year analysis, 1967-71 — A.J. Fox, D.C. Lindars, et al. (1974)

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