Occupational exposure to silica and lung cancer risk in the Netherlands

Our plain-English summary of Occupational exposure to silica and lung cancer risk in the Netherlands, by L. Preller, L.M. van den Bosch, P.A. van den Brandt, et al (Occupational and Environmental Medicine, 2010).

The study

• Authors: L. Preller, L.M. van den Bosch, P.A. van den Brandt, T. Kauppinen, A. Goldbohm
• Journal: Occupational and Environmental Medicine
• Published: 2010;67(10):657-63
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: The lung cancer carcinogenicity of crystalline silica dust remains the subject of discussion. Epidemiological evidence is based on occupational cohort studies and population-based case-control studies. The aim of this study was to assess associations between male lung cancer risk and silica exposure in a population-based cohort study.

Methods: The study was conducted among men aged 55-69 years (n=58 279) from the Netherlands Cohort Study, which included self-reported, life-time job histories. Job titles were linked to the occupational groups of the external Finnish Job Exposure Matrix (FINJEM), including probability and level of silica exposure, each for specific time periods. 1667 incident lung cancer cases with known silica exposure status (210 exposed) were available after 11.3 years of follow-up. Risks were estimated based on a case-cohort design, and using Cox proportional hazards models.

Results: Adjusted for smoking and other confounders, elevated risks were observed for exposure duration (RR 1.65, 95% CI 1.14 to 2.41 for 26-51 years vs no exposure) and cumulative exposure (RR 1.47, 95% CI 0.93 to 2.33 for ≥3 vs <3 mg/m(3).year). Associations with average exposure levels were weaker. Associations were stronger for occupations with an exposure probability of ≥90%. Adjustment for asbestos exposure slightly increased the risk.

Conclusions: Results from this prospective population-based cohort study corroborate the classification of crystalline silica as a lung carcinogen. Associations could not be explained by smoking or by asbestos exposure.

In plain English

This prospective population-based study used the Netherlands Cohort Study, which enrolled men and women aged 55 to 69 in 1986. This analysis covered men only, followed for 11.3 years to December 1997. It compared 1667 men who developed lung cancer with 2034 men from a randomly sampled subcohort. Self-reported lifetime job histories were linked to a Finnish job exposure matrix to estimate exposure to respirable crystalline silica, and 210 cases and 228 subcohort members were rated as ever exposed. After adjustment for smoking and other factors, men exposed for 26 to 51 years had a rate ratio of 1.65 (95% CI 1.14 to 2.41) compared with unexposed men. Cumulative exposure of 3 mg/m3.year or more gave a rate ratio of 1.47 (95% CI 0.93 to 2.33) compared with unexposed men, which was not statistically significant. In a sensitivity analysis, adjusting for estimated asbestos exposure slightly raised the silica estimates. The authors concluded that the results corroborate classifying crystalline silica as a lung carcinogen. They stated they did not adjust for other workplace carcinogens and could not study silicosis, so bias from these could not be ruled out.

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: Prospective population-based cohort study analysed with a case-cohort design (a randomly sampled subcohort used to estimate person-time), using Cox proportional hazards models
• Who was studied: Men aged 55 to 69 at enrolment in the Netherlands Cohort Study (58,279 men; the cohort started September 1986 with 120,852 men and women from 204 municipalities). The men were followed for 11.3 years, to December 1997. After exclusions, 1667 incident primary male lung cancer cases and 2034 male subcohort members were analysed. Of these, 210 cases and 228 subcohort members were ever exposed to silica.
• Exposure: Occupational exposure to respirable crystalline silica (quartz or crystalline silica containing dusts; amorphous silica not included). It was estimated by linking self-reported lifetime job histories to the Finnish Job Exposure Matrix (FINJEM) probability and level of exposure by time period. The most often reported exposed jobs were machine and engine mechanics, construction carpenters, and bricklayers, plasterers and tile setters. In a sensitivity analysis, asbestos exposure (fibres/m3) was estimated in the same way for silica-exposed occupational groups.
• Main results:
  • Entire population, full model adjusted for age, family history of lung cancer, smoking, alcohol and fruit and vegetable intake: 26 to 51 years of silica exposure gave RR 1.65 (95% CI 1.14 to 2.41) versus no exposure. Exposure duration was the only exposure variable that reached statistical significance.
  • Entire population, full model: cumulative exposure of 3 mg/m3.year or more gave RR 1.47 (95% CI 0.93 to 2.33), based on 62 cases. Table 3 states that the reference group is those not exposed to silica. This result was not statistically significant.
  • Entire population, full model: ever exposed to silica gave RR 1.06 (95% CI 0.84 to 1.35), based on 210 exposed cases.
  • Associations with average exposure levels were weaker than those for duration and cumulative exposure.
  • RRs were generally about 0.2 absolute points higher without adjustment for lifestyle factors. The authors attributed this change nearly completely to smoking.
  • In the restricted population (men with jobs of 90% or higher exposure probability, and those with missing or uncodable job data excluded), point estimates were slightly higher than in the entire population. Per Table 3, 26 to 51 years of exposure gave RR 1.75 (95% CI 0.99 to 3.12), and cumulative exposure of 3 mg/m3.year or more gave RR 1.57 (95% CI 0.95 to 2.61), both versus those not exposed to silica.
  • Sensitivity analysis with white-collar workers as the unexposed group: adjustment for asbestos exposure weighted for probability gave RR 2.28 (95% CI 1.06 to 4.87) for the longest silica exposure duration and RR 2.01 (95% CI 1.05 to 3.84) for the highest cumulative silica exposure. These were slightly higher than without adjustment. The unadjusted figures differ between the text and Table 4.
• The authors' conclusion: The authors concluded that their results corroborate the classification of crystalline silica as a lung carcinogen. They stated that the associations could not be explained by smoking or by asbestos exposure.
• Limitations the authors state:
  • There were no actual exposure measurements for the study population; exposure was assigned by job group.
  • Using Finnish exposure data for the Dutch population may have biased average and cumulative exposure estimates.
  • Assigning exposure at the level of broad occupational groups was expected to cause non-differential misclassification, which the authors stated would weaken exposure-response relationships.
  • The authors did not adjust for other occupational carcinogens and could not study the effect of silicosis, so bias from these cannot be ruled out.
  • Most associations were not statistically significant at the 0.05 level. The authors attributed this partly to the relatively small exposed population.
  • Asbestos-exposed occupations could not be identified in the silica-unexposed reference group. The asbestos sensitivity analysis therefore used white-collar workers as the unexposed group.

Topics

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

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Lung Cancer, Crystalline, Cohort Study, Cumulative Exposure, Asbestos Exposure.

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• Socioeconomic status and lung cancer incidence in men in The Netherlands: is there a role for occupational exposure? — A.J. van Loon, R.A. Goldbohm, et al. (1997)
• Occupational exposure to carcinogens and risk of lung cancer: results from The Netherlands cohort study — A.J. van Loon, I.J. Kant, et al. (1997)
• Silica, asbestos, man-made mineral fibers, and cancer — K. Steenland, L. Stayner (1997)
• Silicosis and smoking strongly increase lung cancer risk in silica-exposed workers — N. Kurihara, O. Wada (2004)
• Occupational asbestos exposure and risk of pleural mesothelioma, lung cancer, and laryngeal cancer in the prospective Netherlands cohort study — N.S. Offermans, R. Vermeulen, et al. (2014)
• Asbestos and silica-induced changes in human alveolar macrophage phenotype — A. Holian, M.O. Uthman, et al. (1997)

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