Does exposure to asbestos cause ovarian cancer? A systematic literature review and meta-analysis

Our plain-English summary of Does exposure to asbestos cause ovarian cancer? A systematic literature review and meta-analysis, by A. Reid, N. de Klerk, A.W. Musk (Cancer Epidemiology, Biomarkers & Prevention, 2011).

The study

• Authors: A. Reid, N. de Klerk, A.W. Musk
• Journal: Cancer Epidemiology, Biomarkers & Prevention
• Published: 2011;20(7):1287-95
• Type of article: Meta-analysis, Systematic review
• Cited by: 32 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Introduction: The asbestos and ovarian cancer relationship is not well understood because of small numbers of women exposed to asbestos, small numbers of cases, and misclassification of peritoneal mesothelioma as ovarian cancer on death certificates. The aim of this study was to conduct a meta-analysis to quantify the evidence that exposure to asbestos causes ovarian cancer.

Methods: Fourteen cohort and two case-control studies were identified in Medline searches from 1950 to 2008.

Results: Statistically significant excess mortality was reported in four of the cohort studies, all of which determined their outcomes from the death certificate. Peritoneal mesotheliomas were reported in these studies, two of which reexamined pathology specimens and reported disease misclassification. Exposure-response relationships were inconsistent. When all studies were included in a meta-analysis, the effect size was 1.75 (95% CI, 1.45-2.10) attenuating to 1.29 (95% CI, 0.97-1.73) in studies with confirmed ovarian cancers.

Conclusion: Taken without further analysis, women thought to have ovarian cancer had an increased rate in the meta-analysis if reporting having been exposed to asbestos, compared with reference populations. This result may have occurred because of disease misclassification.

©2011 AACR

In plain English

This article was a systematic literature review and meta-analysis. The authors searched MEDLINE from 1950 to December 2008 and found 14 cohort studies and 2 case-control studies that reported on ovarian cancer in women exposed to asbestos at work or from their general environment. Four of the 14 cohort studies reported a statistically significant excess of ovarian cancer. Combining all 16 studies gave an effect size of 1.75 (95% CI, 1.45–2.10). The 7 studies that reviewed ovarian cancer pathology gave 1.54 (95% CI, 1.22–1.95). The 4 studies of cancer incidence gave 1.29 (95% CI, 0.97–1.73), which was not statistically significant. Twelve cohort studies relied on death certificates, and 8 of them also had cases of peritoneal mesothelioma, which suggested that some peritoneal mesotheliomas may have been misclassified as ovarian cancer. No study showed a statistically significant exposure-response trend. The authors concluded that the excess may reflect how cases were identified. They also judged that the IARC decision to classify asbestos as a cause of ovarian cancer was premature and not wholly supported by the evidence.

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: Systematic literature review and meta-analysis of published cohort and case-control studies, using fixed-effects and random-effects models
• Who was studied: 16 published English-language studies: 14 cohort studies and 2 case-control studies of women exposed to asbestos. The cohorts came from the UK, Germany, Italy, Finland, Poland and Wittenoom (Australia) and ranged from 490 women to 892,591 Finnish female workers. The case-control studies were of Johns Hopkins Hospital patients and Norwegian pulp and paper workers.
• Exposure: Occupational, household and environmental asbestos exposure. Fiber types were: crocidolite only in 3 cohorts, chrysotile only in 2, chrysotile and crocidolite in 5, and mixed fibers including crocidolite in 1. Four studies did not report the fiber type. In the Finnish study, exposure was assigned from job titles using a job exposure matrix.
• Main results:
  • 4 of the 14 cohort studies reported a statistically significant excess of ovarian cancer. Their SMRs ranged from 2.27 (95% CI, 1.04–4.32) to 4.77 (95% CI, 2.18–9.06).
  • All 16 studies combined: fixed-effects size 1.75 (95% CI, 1.45–2.10) and random-effects size 1.80 (95% CI, 1.45–2.24).
  • The 7 studies that reviewed ovarian cancer pathology: effect size 1.54 (95% CI, 1.22–1.95), which was still statistically significant.
  • The 4 studies that examined ovarian cancer incidence (2 case-control and 2 cohort studies): effect size 1.29 (95% CI, 0.97–1.73), not statistically significant.
  • Of the 12 cohort studies that relied on death certificates, 8 also reported cases of peritoneal mesothelioma. The authors took this to suggest that some peritoneal mesotheliomas may have been misclassified as ovarian cancer.
  • Where exposure-response relationships were examined, they were inconsistent, and no study showed a statistically significant trend.
  • A meta-analysis of mesothelioma in 9 of the cohort studies gave a fixed-effects size of 70.9 (95% CI, 61.4–82.0) and a random-effects size of 63.2 (95% CI, 41.9–95.3). The authors found no relationship between the mesothelioma and ovarian cancer SMRs across these studies.
• The authors' conclusion: The authors concluded that the increased rate seen in the meta-analysis may result from the methods used to identify ovarian cancer cases (misclassification on death certificates). They suggested that the IARC decision to classify asbestos exposure as a cause of ovarian cancer was premature and not wholly supported by the evidence.
• Limitations the authors state:
  • Meta-analysis cannot adjust for the quality of the data in the original studies. If those studies misclassified disease, the errors carry into the meta-analysis.
  • Most included studies had small numbers of exposed women and of ovarian cancer cases, which limited the examination of exposure-response relationships.
  • Most studies did not address confounding or other risk factors for ovarian cancer.
  • High loss to follow-up in some studies may have over- or underestimated risk.

Topics

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

Medical terms in this study, explained in our Lexicon: Ovarian Cancer, Systematic Review, Meta-Analysis, Peritoneal Mesothelioma, Death Certificate, Pathology.

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