Kidney cancer and occupational exposure to asbestos: a meta-analysis of occupational cohort studies

Our plain-English summary of Kidney cancer and occupational exposure to asbestos: a meta-analysis of occupational cohort studies, by D. Sali, P. Boffetta (Cancer Causes & Control, 2000).

The study

• Authors: D. Sali, P. Boffetta
• Journal: Cancer Causes & Control
• Published: 2000;11(1):37-47
• Type of article: Meta-analysis
• Cited by: 42 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objective: To study the risk of kidney cancer following asbestos exposure.

Methods: We carried out a meta-analysis of the results of cohort studies of workers predominantly exposed to asbestos. We contacted the authors of 70 cohort studies; published results were available from the reports of 10 cohorts; we obtained the relevant information for an additional 27 cohorts.

Results: The studies included in the analysis comprised a total of 169 kidney cancer deaths and 69 incident cases. The overall pooled standardized mortality ratio (SMR) of kidney cancer was 1.1, with a 95% confidence interval (95% CI) of 0.9-1.3. The pooled SMR was higher for workers with undefined asbestos exposure (SMR 1.2, 95% CI 0.9-1.6) than for workers with either predominant chrysotile (SMR 0.9, 95% CI 0.7-1.3) or some amphibole (SMR 0.96, 95% CI 0.6-1.5) exposure. Studies with published results had higher SMRs than studies for which information was obtained from the authors. Studies with high asbestos exposure and an elevated SMR of lung cancer tended to show an increased risk of kidney cancer.

Conclusions: It is unlikely that asbestos exposure is responsible for an important increase in kidney cancer risk; however, high asbestos exposure might entail a small increase in risk.

In plain English

This meta-analysis pooled kidney cancer results from cohort studies of workers mainly exposed to asbestos. The authors identified 70 cohorts and contacted their researchers. Usable data came from 37 cohorts, much of it previously unpublished, covering 169 kidney cancer deaths and 69 incident cases. Of 34 mortality results, the 26 with at least one kidney cancer death entered the weighted analysis, giving a pooled standardized mortality ratio (random-effects model) of 1.1 (95% CI 0.9 to 1.3). The corresponding figures were 0.9 (0.7 to 1.3) for cohorts exposed predominantly to chrysotile, 1.0 (0.6 to 1.5) for cohorts with some amphibole exposure, and 1.2 (0.9 to 1.6) for cohorts with undefined exposure. Results from published reports were higher (1.5, CI 1.2 to 2.0) than results supplied by study authors (0.9, CI 0.7 to 1.1). Across studies, kidney cancer risk was correlated with lung cancer risk. The authors concluded that most of the evidence pointed toward no association. They added that high exposure might cause some increase in risk, likely smaller than for lung cancer. They noted that kidney cancer data were missing for about half the identified cohorts.

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: Meta-analysis of occupational cohort studies (mortality and incidence), using published results and data obtained directly from the original study authors
• Who was studied: Cohorts of workers with predominant asbestos exposure: asbestos cement and textile workers, miners and millers, friction material, insulator and insulation board manufacturers, and workers compensated for asbestosis. Of 70 cohorts identified, 37 were analyzed, giving 34 kidney cancer mortality results and 6 incidence results, with a total of 169 kidney cancer deaths and 69 incident cases.
• Exposure: Occupational asbestos exposure. Cohorts were grouped as predominant chrysotile (chrysotile more than 90% of total asbestos), some amphibole (amphibole 10% or more of total asbestos), or undefined. Average exposure level was available for some cohorts.
• Main results:
  • For all 34 mortality results combined, 169 deaths were observed against 172.8 expected. The unweighted SMR was 1.0 (CI 0.8 to 1.1).
  • Eight small mortality cohorts with no observed kidney cancer deaths were excluded from the weighted analyses, leaving 26 mortality studies. The random-effects weighted SMR for these was 1.1 (CI 0.9 to 1.3).
  • Mortality cohorts predominantly exposed to chrysotile (15 studies; the weighted estimate used only those with at least one death): unweighted SMR 0.8 (CI 0.6 to 1.1), random-effects SMR 0.9 (CI 0.7 to 1.3).
  • Mortality cohorts with some amphibole exposure (7 studies; the weighted estimate used only those with at least one death): unweighted SMR 0.9 (CI 0.5 to 1.3), random-effects SMR 1.0 (CI 0.6 to 1.5).
  • Mortality cohorts with undefined asbestos exposure (12 studies; the weighted estimates used only those with at least one death): unweighted SMR 1.1 (CI 0.9 to 1.3), random-effects SMR 1.2 (CI 0.9 to 1.6). The fixed-effects SMR for this group was 1.2 (CI 1.0 to 1.5). The authors stated that these estimates were not significantly different from those of the other two groups.
  • Six incidence cohorts: unweighted SIR 0.9 (CI 0.7 to 1.2), random-effects SIR 1.0 (CI 0.7 to 1.3).
  • The pooled estimate from published results was 1.5 (CI 1.2 to 2.0). This was higher than the estimate from results obtained from the study authors (SMR 0.9, CI 0.7 to 1.1).
  • In the 36 non-overlapping studies reporting both outcomes, kidney cancer risk was correlated with lung cancer risk (Pearson coefficient 0.36, p-value 0.03).
  • Exposure-level information existed for 18 mortality and 4 incidence cohorts. It was not enough for a formal dose-response analysis. Some of the studies with the highest kidney cancer risk also reported the highest average exposure.
• The authors' conclusion: The authors concluded that most of the evidence pointed toward no association between asbestos exposure and kidney cancer risk. They stated that a completely negative conclusion was not justified, and that their results were consistent with high asbestos exposure possibly causing some increase in kidney cancer risk, likely smaller than the increase in lung cancer risk.
• Limitations the authors state:
  • Kidney cancer data were unavailable for about half of the identified cohorts, which included 40% of the total number of workers.
  • There was evidence of publication bias. The plot of results suggested a lack of small positive studies, mainly among mortality studies with predominant chrysotile exposure.
  • There was significant heterogeneity among studies with undefined asbestos exposure, which could make the summary estimate for that group invalid.
  • The correlation between kidney and lung cancer risk might reflect factors other than asbestos, such as tobacco smoking.
  • The available exposure information was too crude to allow a formal dose-response analysis.
  • Apart from publication bias, the authors judged that most other possible biases, such as misclassification of exposure or disease, would have pushed results toward false negatives.

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Meta-Analysis, Asbestos Exposure, standardized mortality ratio (SMR), confidence interval, Chrysotile, Amphibole Group, Lung Cancer.

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