Spatial Analysis of Shared Risk Factors between Pleural and Ovarian Cancer Mortality in Lombardy (Italy)

Our plain-English summary of Spatial Analysis of Shared Risk Factors between Pleural and Ovarian Cancer Mortality in Lombardy (Italy), by G. Stoppa, C. Mensi, L. Fazzo, et al (International Journal of Environmental Research and Public Health, 2022).

The study

• Authors: G. Stoppa, C. Mensi, L. Fazzo, G. Minelli, V. Manno, D. Consonni, A. Biggeri, D. Catelan
• Journal: International Journal of Environmental Research and Public Health
• Published: 2022;19(6)
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Asbestos exposure is a recognized risk factor for ovarian cancer and malignant mesothelioma. There are reports in the literature of geographical ecological associations between the occurrence of these two diseases. Our aim was to further explore this association by applying advanced Bayesian techniques to a large population (10 million people).

Methods: We specified a series of Bayesian hierarchical shared models to the bivariate spatial distribution of ovarian and pleural cancer mortality by municipality in the Lombardy Region (Italy) in 2000-2018.

Results: Pleural cancer showed a strongly clustered spatial distribution, while ovarian cancer showed a less structured spatial pattern. The most supported Bayesian models by predictive accuracy (widely applicable or Watanabe-Akaike information criterion, WAIC) provided evidence of a shared component between the two diseases. Among five municipalities with significant high standardized mortality ratios of ovarian cancer, three also had high pleural cancer rates. Wide uncertainty was present when addressing the risk of ovarian cancer associated with pleural cancer in areas at low background risk of ovarian cancer.

Conclusions: We found evidence of a shared risk factor between ovarian and pleural cancer at the small geographical level. The impact of the shared risk factor can be relevant and can go unnoticed when the prevalence of other risk factors for ovarian cancer is low. Bayesian modelling provides useful information to tailor epidemiological surveillance.

In plain English

This geographical (ecological) study compared ovarian and pleural cancer death rates among women in 1546 municipalities of Lombardy, Italy, from 2000 to 2018. Asbestos exposure was not measured; pleural cancer served as its stand-in. There were 2070 pleural cancer deaths and 10,462 ovarian cancer deaths. Using Bayesian statistical models, the authors found pleural cancer strongly clustered geographically and ovarian cancer less so. The best-supported models included a component shared by both diseases, and the shared clustering pattern highlighted areas with known asbestos exposure. Of five municipalities with significantly high ovarian cancer death rates, three also had high pleural cancer rates. In Broni, which had very high pleural cancer mortality, ovarian cancer deaths were near the regional average (13 observed, 13.37 expected), and estimates of its ovarian cancer risk varied between models. The authors concluded there was evidence of a shared risk factor, whose effect can go unnoticed where other ovarian cancer risk factors are uncommon. They noted the ecological fallacy inherent in grouped data and possible misclassification of pleural cancer deaths.

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: Ecological (geographical) study of mortality by municipality, analysed with a series of Bayesian hierarchical spatial models, including models with components shared by the two diseases
• Who was studied: Women who died of ovarian cancer (10,462 deaths) or pleural cancer (2070 deaths) in the 1546 municipalities of the Lombardy Region, Italy, 2000 to 2018; death records from the Italian National Institute of Statistics (ISTAT)
• Exposure: Asbestos exposure was not measured directly. Pleural cancer mortality (including pleural mesothelioma) was used as a proxy for asbestos exposure, and the shared model components were interpreted as proxies of the prevalence of asbestos exposure.
• Main results:
  • There were 2070 pleural cancer deaths among women in Lombardy, 2000 to 2018.
  • There were 10,462 ovarian cancer deaths, with municipal SMRs ranging from 0 to 19.15.
  • Pleural cancer had a strongly spatially structured (clustered) pattern. Ovarian cancer had a more complex pattern, with clustering and random variation almost equally represented.
  • Five municipalities had ovarian cancer SMRs above the regional average (one-sided p less than 0.001): Rosate, Bovegno, Capriate SG, Pedrengo and Calcio. Three of these also had high pleural cancer SMRs; for example, Calcio had an ovarian cancer SMR of 2.87 and a pleural cancer SMR of 8.52.
  • The best-supported model (M7, WAIC 5116.985) included both disease-specific and shared components. The model with no shared components (M1, WAIC 5167.727) had worse support.
  • Under the simpler model 4, the shared clustering component highlighted areas with known asbestos exposure.
  • From the scaling parameters (delta 0.265, 95% CrI 0.197 to 0.342; omega 0.659, 95% CrI 0.432 to 1.036), the authors stated that the relative risk of pleural cancer for asbestos exposure was four times (shared clustering component) or 1.5 times (shared heterogeneity component) the relative risk of ovarian cancer.
  • In Broni, pleural cancer SMR was 18.3 (51 observed, 2.79 expected), the second highest in the region.
  • In Broni, the ovarian cancer SMR was 0.97 (13 observed, 13.37 expected).
  • Model estimates of ovarian cancer risk in Broni differed between models: RR 1.23 (95% CrI 1.01; 1.49) under model 4, 0.93 (95% CrI 0.80; 1.06) under model 1, and 1.06 (95% CrI 0.80; 1.37) under model 7.
  • A supplementary analysis of malignant mesothelioma of all sites (2439 deaths) together with ovarian cancer gave quite similar results.
• The authors' conclusion: The authors concluded that there was evidence of a shared risk factor between ovarian and pleural cancer mortality at small geographical level. They also concluded that the burden of ovarian cancer due to asbestos exposure can go unnoticed in small areas at low background risk of ovarian cancer.
• Limitations the authors state:
  • The ecological fallacy is inherent in analyses of aggregate (grouped) data.
  • Pleural cancer mortality can be subject to misclassification.
  • The contributions of the different random terms are hard to separate; the authors describe the models as overparametrized, with an identifiability issue.
  • Model robustness was lower in the Broni area, and the authors advised caution in drawing inferences about ovarian cancer risk in Broni.

Topics

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

Medical terms in this study, explained in our Lexicon: Ovarian Cancer, Asbestos Exposure, Malignant Mesothelioma, standardized mortality ratio (SMR).

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