Occupational exposure to asbestos and ovarian cancer: a meta-analysis

Our plain-English summary of Occupational exposure to asbestos and ovarian cancer: a meta-analysis, by M.C. Camargo, L.T. Stayner, K. Straif, et al (Environmental Health Perspectives, 2011).

The study

• Authors: M.C. Camargo, L.T. Stayner, K. Straif, M. Reina, U. Al-Alem, P.A. Demers, P.J. Landrigan
• Journal: Environmental Health Perspectives
• Published: 2011;119(9):1211-7
• Type of article: Meta-analysis
• Cited by: 84 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objective: A recent Monographs Working Group of the International Agency for Research on Cancer (IARC) concluded that there is sufficient evidence for a causal association between exposure to asbestos and ovarian cancer. We performed a meta-analysis to quantitatively evaluate this association.

Data Sources: Searches of PubMed and unpublished data yielded a total of 18 cohort studies of women occupationally exposed to asbestos.

Data Extraction: Two authors independently abstracted data; any disagreement was resolved by consulting a third reviewer.

Data Synthesis: All but one study reported standardized mortality ratios (SMRs) comparing observed numbers of deaths with expected numbers for the general population; the exception was a study that reported standardized incidence ratios. For simplicity, we refer to all effect estimates as SMRs. The overall pooled SMR estimate for ovarian cancer was 1.77 (95% confidence interval, 1.37-2.28), with a moderate degree of heterogeneity among the studies (I2 = 35.3%, p = 0.061). Effect estimates were stronger for cohorts compensated for asbestosis, cohorts with estimated lung cancer SMRs > 2.0, and studies conducted in Europe compared with other geographic regions. Effect estimates were similar for studies with and without pathologic confirmation, and we found no evidence of publication bias (Egger's test p-value = 0.162).

Conclusions: Our study supports the IARC conclusion that exposure to asbestos is associated with increased risk of ovarian cancer.

In plain English

This meta-analysis combined 15 published reports on women exposed to asbestos at work with ovarian cancer results supplied by investigators of three other published cohort studies. These covered 20 populations, mostly European, including textile, cement, mining and gas mask workers. Overall, the pooled standardized mortality ratio (SMR) for ovarian cancer was 1.77 (95% CI 1.37–2.28). Pooled SMRs were 4.67 (95% CI 2.28–9.54) for three cohorts compensated for asbestosis versus 1.60 (1.28–2.00) for the rest; 2.25 (1.64–3.07) for 13 cohorts with lung cancer SMRs above 2.0 versus 1.18 (0.81–1.72) for four at 2.0 or below; and 1.95 (1.51–2.51) for European versus 0.92 (0.54–1.59) for United States and Australian cohorts. Six high-exposure groups had a pooled SMR of 2.78 (1.36–5.66). Assuming 20% of ovarian cancer cases in each study were misdiagnosed peritoneal mesothelioma and removing them gave an SMR of 1.42 (1.11–1.82). The authors could not account for non-work risk factors other than age. They concluded their results support IARC's conclusion that asbestos exposure is causally associated with increased ovarian cancer risk.

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 cohort studies of women occupationally exposed to asbestos
• Who was studied: 15 published reports that met the inclusion criteria, plus previously unreported ovarian cancer results supplied by investigators of three other published cohort studies. Together these were 18 articles covering 20 distinct cohorts of asbestos-exposed women. Fifteen studies were from Europe, two from the United States and one from Australia. The literature was searched up to March 2010.
• Exposure: Occupational asbestos exposure in asbestos cement and textile workers, miners and millers, friction material, insulator and insulation board manufacturers, gas mask assemblers, and workers compensated for asbestosis. Fiber types were chrysotile, crocidolite or mixed.
• Main results:
  • The overall pooled SMR for ovarian cancer among asbestos-exposed women was 1.77 (95% CI, 1.37–2.28), with moderate heterogeneity between studies.
  • The three cohorts compensated for asbestosis had a pooled SMR of 4.67 (95% CI, 2.28–9.54).
  • Cohorts not compensated for asbestosis had a pooled SMR of 1.60 (95% CI, 1.28–2.00).
  • The 13 cohorts with a lung cancer SMR above 2.0 had a pooled ovarian cancer SMR of 2.25 (95% CI, 1.64–3.07).
  • Per Table 2, the four cohorts with a lung cancer SMR of 2.0 or less had a pooled ovarian cancer SMR of 1.18 (95% CI, 0.81–1.72). The three cohorts with no lung cancer SMR data had a pooled SMR of 1.15 (95% CI, 0.73–1.82).
  • European cohorts had a pooled SMR of 1.95 (95% CI, 1.51–2.51). Cohorts from the United States and Australia had a pooled SMR of 0.92 (95% CI, 0.54–1.59).
  • Cohorts exposed predominantly to crocidolite (pooled SMR 2.18) or to mixed asbestos (2.00) showed larger SMRs than chrysotile-exposed cohorts (1.40; 95% CI, 0.88–2.21). The authors described this variation by fiber type as suggestive but not statistically significant.
  • Six high-exposure groups had a pooled SMR of 2.78 (95% CI, 1.36–5.66).
  • In a sensitivity analysis, the authors assumed that 20% of the cases were misclassified as ovarian cancer and removed 20% of ovarian cancer cases from every study. The pooled SMR was then 1.42 (95% CI, 1.11–1.82).
  • Egger's test (p = 0.162) gave little evidence of publication bias.
• The authors' conclusion: The authors concluded that their results support IARC's conclusion that asbestos exposure is causally associated with an increased risk of ovarian cancer. They judged it unlikely that the results are fully explained by misclassification of peritoneal mesothelioma as ovarian cancer, or by other bias and confounding.
• Limitations the authors state:
  • The analysis could not account for non-occupational risk factors for ovarian cancer other than age.
  • Only two studies had pathologic confirmation, which limited the comparison of studies with and without it.
  • Differing definitions of exposure duration and latency prevented a proper dose-response evaluation.
  • The studies came mainly from developed areas, particularly Europe.
  • Some published cohort studies did not report findings for ovarian cancer, or reported only on cancers of the female genital organs.

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: Occupational Exposure, Ovarian Cancer, Meta-Analysis, IARC, standardized mortality ratio (SMR), Standardized Incidence Ratio (SIR), confidence interval, Lung Cancer.

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