A Cohort Study on Cancer Incidence among Women Exposed to Environmental Asbestos in Childhood with a Focus on Female Cancers, including Breast Cancer

Our plain-English summary of A Cohort Study on Cancer Incidence among Women Exposed to Environmental Asbestos in Childhood with a Focus on Female Cancers, including Breast Cancer, by S.B. Dalsgaard, E.T. Würtz, J. Hansen, et al (International Journal of Environmental Research and Public Health, 2022).

The study

• Authors: S.B. Dalsgaard, E.T. Würtz, J. Hansen, O.D. Røe, Ø. Omland
• Journal: International Journal of Environmental Research and Public Health
• Published: 2022;19(4)
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: To examine the risk of cancer in former school children exposed to environmental asbestos in childhood with a focus on female cancers, including breast cancer.

Methods: We retrieved a cohort of females (n = 6024) attending four schools located in the neighborhood of a large asbestos cement plant in Denmark. A reference cohort was frequency-matched 1:9 (n = 54,200) in sex and five-year age intervals. Using Danish registries, we linked information on historical employments, relatives' employments, cancer, and vital status. We calculated standardized incidence rates (SIRs) for all and specific cancers, comparing these rates with the reference cohort. Hazard ratios were calculated for selected cancers adjusted for occupational and familial asbestos exposure.

Results: For cancer of the corpus uteri (SIR 1.29, 95% CI 1.01-1.66) and malignant mesothelioma (SIR 7.26, 95% CI 3.26-16.15), we observed significantly increased incidences. Occupationally, asbestos exposure had a significantly increased hazard ratio for cancer in the cervix, however, a significantly lower risk of ovarian cancer. The overall cancer incidence was similar to that of the reference cohort (SIR 1.02, 95% CI 0.96-1.07). The risk of cancer of the lung was increased for those exposed to occupational asbestos, those with family members occupationally exposed to asbestos and for tobacco smokers.

Conclusions: In our study, environmental asbestos exposure in childhood is associated with an increased risk of cancer of the corpus uteri and malignant mesothelioma in women.

In plain English

This Danish register-based cohort study followed 6,024 women, born 1940 to 1970, who as children attended schools 100 to 750 m from the asbestos cement plant in Aalborg. The plant's asbestos was 89% chrysotile. The women were compared with 54,200 women from across Denmark matched by birth-year group, and were followed to 2015 (median 51 years). The school group had more cancer of the corpus uteri (body of the uterus) than expected (SIR 1.29, 95% CI 1.01–1.66) and more malignant mesothelioma (SIR 7.26, 95% CI 3.26–16.15). Their overall cancer incidence (SIR 1.02, 95% CI 0.96–1.07) and breast cancer incidence (SIR 0.98, 95% CI 0.89–1.09) were similar to the reference group. Across both groups, women with their own occupational asbestos exposure had a higher hazard ratio for cervical cancer (1.55, 95% CI 1.03–2.35) but a lower one for ovarian cancer (0.25, 95% CI 0.15–0.41). Lung cancer risk was higher with own or family occupational exposure. The authors concluded that the school group had an increased risk of corpus uteri cancer and mesothelioma, possibly partly due to lifestyle factors. They noted that environmental exposure was judged only from 7th grade school attendance.

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: Retrospective register-based cohort study comparing a school cohort with a frequency-matched national reference cohort, using standardized incidence ratios and Cox regression
• Who was studied: 6,024 women who, as pupils born 1940–1970, attended a school 100 to 750 m from the asbestos cement plant in Aalborg, Denmark. They were compared with 54,200 women from across Denmark, frequency-matched 1:9 by sex and five-year birth-year group. Cancer follow-up ran to 31 December 2015, with a median follow-up of 51 years.
• Exposure: Environmental asbestos exposure in childhood from attending school (and likely living) near Denmark's only asbestos cement plant, which manufactured about 620,000 tons of asbestos (89% chrysotile). Own and family occupational asbestos exposure were assessed separately with a job exposure matrix.
• Main results:
  • School cohort women had a significantly increased incidence of cancer of the corpus uteri: 61 observed vs 47.18 expected, SIR 1.29, 95% CI 1.01–1.66
  • School cohort women had a significantly increased incidence of malignant mesothelioma: 6 observed vs 0.83 expected, SIR 7.26, 95% CI 3.26–16.15
  • Overall cancer incidence in the school cohort was similar to the reference cohort: SIR 1.02, 95% CI 0.96 to 1.07, based on 1331 primary cancers among the 6024 women
  • Breast cancer incidence in the school cohort was similar to the reference cohort: 343 observed vs 348.30 expected, SIR 0.98, 95% CI 0.89 to 1.09
  • Fewer ovarian cancer cases than expected occurred in the school cohort: SIR 0.72, 95% CI 0.52–1.01
  • After adjustment for occupational and familial occupational asbestos exposure, the hazard ratio for corpus uteri cancer in the environmental exposure (school) group was HR 1.32, 95% CI 1.02–1.75
  • In the regression analysis, malignant mesothelioma was associated with environmental asbestos exposure in childhood (HR 7.41, 95% CI 2.49–22.06). This result was not adjusted because there were few observations in the occupational and familial exposure groups.
  • In the regression analysis covering both cohorts, women with occupational asbestos exposure had a significantly increased hazard ratio for cervical cancer: HR 1.55, 95% CI 1.03–2.35
  • Women with occupational asbestos exposure had a significantly lower hazard ratio for ovarian cancer: HR 0.25, 95% CI 0.15–0.41
  • Overall lung cancer incidence was not elevated in the school cohort (SIR 1.11, 95% CI 0.93 to 1.32)
  • Lung cancer hazard was increased for women with their own occupational asbestos exposure: HR 1.38, 95% CI 1.06–1.80
  • Lung cancer hazard was increased for women with family members occupationally exposed to asbestos: HR 1.23, 95% CI 1.06–1.43
  • Lung cancer hazard was increased for women with the smoking proxy (a COPD diagnosis): HR 3.55, 95% CI 3.05–4.15
• The authors' conclusion: The authors concluded that their study revealed an increased risk of cancer of the corpus uteri and malignant mesothelioma in the female former school children exposed to environmental asbestos. They added that the increased risk may partly have been due to lifestyle and behavioral characteristics, but that a potential effect of environmental asbestos exposure on some cancers cannot be discarded.
• Limitations the authors state:
  • Environmental asbestos exposure was estimated solely from 7th grade school attendance, not from personal, monitored measurement
  • There was no information on environmental asbestos exposure before or after 7th grade school attendance
  • There was no information on the women's childbirth experience or income, both of which are confounders for some female cancers
  • Only asbestos and tobacco smoking were taken into account, so co-exposure to other carcinogens cannot be ruled out
  • Using a COPD diagnosis as a proxy for smoking is unlikely to control for all smoking-related confounding, and some misclassification is unavoidable
  • The authors noted that the corpus uteri finding could be incidental, since an increased risk would also be expected among women with occupational asbestos exposure
  • The authors stated that the increased risk may partly have been due to lifestyle and behavioral characteristics

Topics

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

Medical terms in this study, explained in our Lexicon: Cohort Study, Asbestos-Cement, Incidence, Hazard Ratio, Asbestos Exposure, Malignant Mesothelioma, Ovarian Cancer.

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