Asbestos and ovarian cancer: examining the historical evidence

Our plain-English summary of Asbestos and ovarian cancer: examining the historical evidence, by B. Slomovitz, C. de Haydu, M. Taub, et al (International Journal of Gynecological Cancer, 2021).

The study

• Authors: B. Slomovitz, C. de Haydu, M. Taub, R.L. Coleman, B.J. Monk
• Journal: International Journal of Gynecological Cancer
• Published: 2021;31(1):122-128
• Type of article: Historical article, Review
• Cited by: 22 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestos recently returned to the spotlight when Johnson & Johnson halted sales of baby powder due to lawsuits claiming that the talc in baby powder may have been contaminated with asbestos, which has been linked to the risk of ovarian cancer development. Although talc and asbestos have some structural similarities, only asbestos is considered causally associated with ovarian cancer by the WHO's International Agency for Research on Cancer. While it is useful to understand the types and properties of asbestos and its oncologic biology, the history of its association with ovarian cancer is largely based on retrospective observational studies in women working in high asbestos exposure environments. In reviewing the literature, it is critical to understand the distinction between associative risk and causality, and to examine the strength of association in the context of how the diagnosis of ovarian cancer is made and how the disease should be distinguished from a similar appearing but unrelated neoplasm, malignant mesothelioma. Based on contextual misinterpretation of these factors, it is imperative to question the International Agency for Research on Cancer's assertion that asbestos has a clear causal inference to ovarian cancer. This has important clinical implications in the way patients are conceivably counseled and provides motivation to continue research to improve the understanding of the association between asbestos and ovarian cancer.

© IGCS and ESGO 2021. No commercial re-use. See rights and permissions. Published by BMJ.

In plain English

This review re-examined the evidence behind the International Agency for Research on Cancer (IARC) position that asbestos causes ovarian cancer. The authors focused on the five cohort studies IARC relied on, which followed women with heavy work exposure to asbestos in England and Italy. Those studies reported raised standardized mortality ratios for ovarian cancer; in one gas mask factory study, women who used crocidolite had 2.75 (95% CI 1.42 to 4.81). The authors' main concern was that peritoneal mesothelioma can be mistaken for ovarian cancer, and that tumor tissue was rarely re-checked. In the three studies that reviewed any pathology, 18 samples were examined from cohorts totaling 1977 patients, and five (28%) had been misdiagnosed. The authors also described a meta-analysis in which the overall ratio of 1.75 (95% CI 1.45 to 2.10) fell to a non-significant 1.29 (95% CI 0.97 to 1.7) when limited to studies that accounted for pathology. They concluded the association is weak and inconsistent and questioned IARC's causal conclusion. They acknowledged the evidence could also be read the other way, and called for further research.

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: Narrative review of published studies, focused on the evidence IARC used to conclude that asbestos causes ovarian cancer
• Who was studied: Published studies. The main focus was the five cohort mortality studies cited by the IARC 2012 Working Group: women exposed to asbestos at work in English gas mask factories and an East London asbestos factory, and in Italy (women compensated for asbestosis, and asbestos cement workers). The review also covered other studies from Finland, Norway and Italy, and a meta-analysis.
• Exposure: Heavy occupational asbestos exposure: crocidolite and chrysotile in wartime gas mask manufacture, and mixed fiber types in factories and asbestos cement work. The review also discussed talc as a possible carrier of asbestos.
• Main results:
  • The authors reported that IARC's finding of a 'clearly established' causal association was based mainly on five cohort studies.
  • In the Acheson et al study the authors reviewed, the 757 women exposed to crocidolite had an ovarian cancer SMR of 2.75 (95% CI 1.42 to 4.81). The 570 women exposed to chrysotile had an SMR of 1.48 (95% CI 0.48 to 3.44).
  • Three of the IARC-cited studies used any pathologic review. Across those three studies, 1977 patients were available and 18 samples were reviewed.
  • Of those 18 reviewed samples, 5 (28%) had been misdiagnosed. The authors called this a high rate of misclassification.
  • The authors stated that none of the studies IARC relied on described their methods for histology review.
  • In the Reid et al meta-analysis the authors described, all available studies combined gave an SMR of 1.75 (95% CI 1.45 to 2.10) compared with reference populations.
  • In the same meta-analysis, studies that accounted for pathology gave a non-significant SMR of 1.29 (95% CI 0.97 to 1.7).
  • In a Finnish registry study the authors described, even women with the highest asbestos exposure did not have a significantly increased risk of ovarian cancer.
• The authors' conclusion: The authors concluded that the observed statistical association between asbestos and ovarian cancer is weak and inconsistent. They added that, without expert pathologic review, a clear causal association is extremely difficult to establish, and they called for further research and improved study design.
• Limitations the authors state:
  • The authors acknowledged that the same evidence could support the opposite reading: ovarian cancer rates could be higher than reported, with some peritoneal mesothelioma cases actually being misdiagnosed ovarian cancers.

Topics

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

Medical terms in this study, explained in our Lexicon: Ovarian Cancer, Talc, Asbestos Exposure, Neoplasm, Malignant Mesothelioma.

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• Benign cystic peritoneal mesothelioma incorrectly diagnosed as an ovarian borderline mucinous tumor of intestinal type at transvaginal preoperative ultrasound evaluation — A.C. Testa, G.F. Zannoni, et al. (2011)
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