Asbestos exposure and haematological malignancies: a Danish cohort study

Our plain-English summary of Asbestos exposure and haematological malignancies: a Danish cohort study, by E.T. Würtz, J. Hansen, O.D. Røe, et al (European Journal of Epidemiology, 2020).

The study

• Authors: E.T. Würtz, J. Hansen, O.D. Røe, Ø. Omland
• Journal: European Journal of Epidemiology
• Published: 2020;35(10):949-960
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Environmental asbestos exposure and occupational asbestos exposure increase the risk of several types of cancer, but the role of such exposures for haematological malignancies remains controversial. We aimed to examine the risk of haematological malignancies: first, in subjects exposed early in life, independently of any occupational exposure occurring later; second, in subjects exposed occupationally. We established an environmentally exposed cohort from four schools located near the only former asbestos cement production plant in Denmark. We identified nearly all pupils in the seventh grade and created an age and sex-matched 1:9 reference cohort from the Danish Central Population Register. Participants were born 1940-1970 and followed up in national registers until the end of 2015. Occupational asbestos exposure was assessed for all participants using two different job exposure matrices. The school cohort included 12,111 participants (49.7% girls) and the reference cohort 108,987 participants. Eight subgroups of haematological malignancy were identified in the Danish Cancer Registry. These cases were analysed for combined overall haematological malignancy, a combined subgroup of lymphomas and a combined subgroup of leukaemias. The data were analysed using Cox regression (hazard ratios (HR)) including other cancers and death as competing risks. Haematological malignancy was identified in 1125 participants. The median follow-up was 49.3 years (0.1-63.4). Early environmental asbestos exposure was not associated with an increased risk of haematological malignancy. Long-term occupational asbestos exposure was associated with overall haematological malignancy (HR 1.69, 95% CI 1.04-2.73); in particular for the leukaemia subgroup (HR 2.14, 95% CI 1.19-3.84). This large follow-up study suggests that long-term occupational asbestos exposure is associated with increased leukaemia risk. However, further studies are needed to confirm these observations.

In plain English

This Danish register-based cohort study examined whether asbestos exposure was linked to blood cancers (haematological malignancies). The authors identified 12,111 people born 1940–1970 who attended seventh grade at four Aalborg schools 100–750 m from Denmark's only former asbestos cement plant. They compared them with 108,987 age- and sex-matched people from all over Denmark, following both groups in national registers until the end of 2015. Occupational asbestos exposure was estimated from employment records using two job exposure matrices. Blood cancer was found in 1125 participants. The school group showed no evidence of a difference from the comparison group (standardised incidence ratio 0.94, 95% CI 0.78–1.13). Working more than 15 years in jobs classed as asbestos-exposed under one matrix was associated with overall blood cancer (hazard ratio 1.69, 95% CI 1.04–2.73). Working more than 10 years in such jobs was associated with leukaemia (hazard ratio 2.14, 95% CI 1.19–3.84). The lymphoma association was not statistically significant, and numbers of exposed cases were small. The authors concluded that long-term occupational exposure may be a risk factor for leukaemia, and that further studies are needed to confirm this.

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: a school cohort compared with an age- and sex-matched (1:9) reference cohort, analysed with standardised incidence ratios and Cox regression (other cancers and death as competing risks)
• Who was studied: 12,111 pupils (49.7% girls) who attended seventh grade at four schools in Aalborg, Denmark, and 108,987 reference participants from all over Denmark who had not attended these schools; born 1940–1970, followed in national registers until the end of 2015 (median follow-up 49.3 years)
• Exposure: Environmental exposure: attending seventh grade at one of four primary schools 100–750 m from, and in the dominant wind direction of, the Danish Eternit Fabric Ltd asbestos cement plant. According to an earlier report the authors cite, the plant used mainly chrysotile from Cyprus (89%), supplemented with amosite (10%) and crocidolite (1%). Occupational exposure was assessed from pension-register employment histories using two job exposure matrices (JEM1: jobs with more than 50% of workers exposed; JEM2: prevalence multiplied by exposure level, cut-off 0.1 or more), including analyses of more than 10 and more than 15 years of exposure.
• Main results:
  • Haematological malignancy was identified in 1125 participants.
  • Standardised incidence ratios showed no evidence of a difference between the school cohort and the reference cohort for overall haematological malignancy (SIR 0.94, 95% CI 0.78–1.13), lymphoma (SIR 0.83, 95% CI 0.65–1.05) or leukaemia (SIR 1.13, 95% CI 0.83–1.53).
  • In Cox regression, estimates for childhood environmental exposure (attending the schools near the plant) were essentially null for all outcomes, whichever job exposure matrix was used.
  • Long-term occupational asbestos exposure was associated with overall haematological malignancy (HR 1.69, 95% CI 1.04–2.73; JEM2 more than 15 years, 17 exposed cases) and with leukaemia (HR 2.14, 95% CI 1.19–3.84; JEM2 more than 10 years, 12 exposed cases).
  • For lymphoma, the association with occupational asbestos exposure was not statistically significant.
  • The numbers of exposed cases were small in both job exposure matrix models for long-term occupational exposure.
  • In a sensitivity analysis restricted to participants born after January 1946 (n = 85,614), estimates for occupational asbestos exposure were higher (for example, overall haematological malignancy with JEM2 more than 10 years: HR 2.58, 95% CI 1.57–4.26, rather than 1.47, 95% CI 1.00–2.16).
  • Males had a significantly increased risk of haematological malignancy in all outcomes, with hazard ratios from 1.41 to 1.65.
• The authors' conclusion: The authors concluded that their study does not support an association between environmental asbestos exposure in childhood and haematological malignancies, but that long-term occupational asbestos exposure may be a risk factor for leukaemia. They stated that further studies are needed to confirm these observations.
• Limitations the authors state:
  • Environmental exposure was coarsely classified. Only seventh-grade school records were available, and the authors did not know how long children attended the schools or lived near the plant.
  • Domestic exposure (for example, a father working at the plant) was not included.
  • Employment records covered only wage earners, not self-employment.
  • Occupational exposure was assigned at the company level, mixing white-collar and blue-collar workers, which causes misclassification.
  • There were few cases. The study lacked power to stratify further by solely environmental, solely occupational and combined exposure, and a healthy worker effect may have contributed.
  • Smoking information was missing, and the leukaemia association might be skewed by socio-economic factors or smoking, possibly overestimating it.

Topics

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Cohort Study, Occupational Exposure, Asbestos-Cement, Cancer Registry, Hazard Ratio.

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