Difficulties in establishing a causal link between chemical exposures and cancer cannot be overcome by court assessments

Our plain-English summary of Difficulties in establishing a causal link between chemical exposures and cancer cannot be overcome by court assessments, by T.A. Dragani (Human & Experimental Toxicology, 2020).

The study

• Author: T.A. Dragani
• Journal: Human & Experimental Toxicology
• Published: 2020;39(8):1095-1107
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Scientific data are often used in lawsuits to prove, or dismiss, causation by a claimed factor of a claimed disease. Recent media reports of million-dollar compensations awarded to some cancer patients who had been exposed to certain chemical substances motivated me to examine how solid the causal links really were. Here, I discuss the limitations of epidemiological research on cancer causation and highlight how new knowledge of cancer genetics makes it unrealistic to expect that cancer causation can be clearly demonstrated. I then present two exposure-cancer cases, namely talcum powder-ovarian cancer and glyphosate-non-Hodgkin lymphoma, that led to civil lawsuits decided, in the United States, in favor of the claimants. Both these cancers have several risk factors, among which the claimed exposure presents only a minor, if any, increased risk. Through these cases, I explain why the use of epidemiological data is inappropriate to define causal associations in complex diseases like cancer. I close by suggesting a fairer approach, called proportional liability, to resolving future cancer litigation cases.

In plain English

This article is a narrative review and commentary, not a new study. The author discussed limits of epidemiological research for showing that an exposure caused cancer in an individual. The author then examined two exposure–cancer pairs that led to US civil lawsuits decided for the claimants: genital talcum powder use and ovarian cancer (talc can be contaminated with asbestos), and glyphosate and non-Hodgkin lymphoma. On asbestos, the author cited two meta-analyses of ovarian cancer. One reported a pooled standardized mortality ratio of 1.77 (95% CI 1.37–2.28). The other reported 1.75 (95% CI 1.45–2.10) but found no significant association in four incidence studies, and its authors suggested peritoneal mesothelioma may have been misclassified as ovarian cancer. The author noted rodent studies in which lifetime diets containing 1% amosite or crocidolite had no carcinogenic effects. The author judged that Hill's causation features were not met for talc and ovarian cancer. The author concluded that a causal link with asbestos or asbestos-contaminated talcum powder is almost impossible to establish in an individual, and proposed "proportional liability" for future cases.

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 and commentary by a single author, discussing published epidemiological and experimental studies and two sets of US court cases; no new data were collected
• Who was studied: No study population of its own; the author reviewed published studies and meta-analyses on two exposure–cancer pairs that were the subject of US civil lawsuits
• Exposure: Asbestos exposure (by any route) and genital use of talcum powder, which can be contaminated with asbestos, in relation to ovarian cancer; and the herbicide glyphosate in relation to non-Hodgkin lymphoma
• Main results:
  • Reviewed finding (Camargo et al. meta-analysis, cited by the author): the pooled standardized mortality ratio for ovarian cancer with asbestos exposure was 1.77 (95% CI 1.37–2.28)
  • Reviewed finding (Reid et al. meta-analysis, cited by the author): the meta-SMR was 1.75 (95% CI 1.45–2.10). In a subanalysis of four studies of cancer incidence, there was no significant association between asbestos exposure and ovarian cancer risk (effect size 1.29; 95% CI 0.97–1.73). Those authors suggested the associations may reflect peritoneal mesothelioma misclassified as ovarian cancer
  • Reviewed finding: a pooled analysis of eight case–control studies found an odds ratio of 1.24 (95% CI 1.15–1.33) for epithelial ovarian cancer with genital powder use. In two 2018 meta-analyses, cohort studies showed no significant associations
  • Reviewed finding: rodent studies from the late 1970s found that a lifetime diet containing 1% amosite or crocidolite had no carcinogenic effects
  • The author's assessment was that Hill's features of causation were not fulfilled for talc exposure and ovarian cancer (temporality rated 'not certain'). The author also judged that none was fulfilled for glyphosate and non-Hodgkin lymphoma
• The authors' conclusion: The author concluded that, in an individual with ovarian cancer, it is almost impossible to establish a causal link with asbestos or asbestos-contaminated talcum powder. Under the 'more likely than not' burden of proof, the author held that talcum powder use cannot be considered a cause of ovarian cancer, and proposed 'proportional liability' as a fairer approach for future cancer litigation
• Limitations the authors state:
  • The author noted that courts would find it extremely difficult to apply proportional liability across the many risk factors that may contribute to a cancer

Topics

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

Medical terms in this study, explained in our Lexicon: Causation, Ovarian Cancer.

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