Occupational exposures of firefighting and urinary tract cancer risk among men in the Norwegian Fire Departments Cohort

Our plain-English summary of Occupational exposures of firefighting and urinary tract cancer risk among men in the Norwegian Fire Departments Cohort, by N. Marjerrison, T.K. Grimsrud, J. Hansen, et al (Occupational and Environmental Medicine, 2023).

The study

• Authors: N. Marjerrison, T.K. Grimsrud, J. Hansen, J.I. Martinsen, K.C. Nordby, R. Olsen, M.B. Veierød, K. Kjærheim
• Journal: Occupational and Environmental Medicine
• Published: 2023;80(12):659-666
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: Increased risks of bladder cancer and mesothelioma were the strongest evidence for the recent reclassification of firefighting as carcinogenic (Group 1) by the International Agency for Research on Cancer. Our study aim was to develop indicators for specific firefighting exposures and examine associations with urinary tract cancer (UTC), including bladder cancer.

Methods: We developed indicators for exposure from employment at a fire department or in firefighting jobs, to fire and smoke, and to diesel exhaust for men in the Norwegian Fire Departments Cohort (n=4250). Incident UTC cases were obtained from the Cancer Registry of Norway (1960-2021). Poisson regression was used to estimate incidence rate ratios (IRR) with cumulative exposures grouped into tertiles (reference: lowest exposed tertile) with 0-year, 10-year and 15-year lagging of exposures.

Results: During 125 090 person-years of follow-up, there were 76 cases of UTC. IRRs were mostly non-significantly increased in the middle tertile and at or below 1 in the highest tertile for total duration of employment, number of fires attended and fire exposure score with and without lags. In the middle tertile for diesel exhaust exposure, UTC risk was elevated over twofold with 10-year (IRR 2.27, 95% CI 1.22 to 4.20) and 15- year (2.21, 1.18 to 4.16) lags, and near 1 in the highest tertile. Findings for bladder cancer were similar to those for UTC.

Conclusions: Dose-response associations between the exposure indicators and UTC were not observed. Future studies using the indicators with more cases are needed.

© Author(s) (or their employer(s)) 2023. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.

In plain English

This study followed 4250 men who had worked at Norwegian fire departments, using national registries for 1960 to 2021. The authors built measures of firefighting work: years employed, years in fire-exposed jobs, fires attended, fire and smoke scores that took breathing apparatus into account, and a fire-station diesel exhaust score. They compared urinary tract cancer rates across the lowest, middle and highest thirds of each measure. There were 76 cases, 64 of them bladder cancer. For years employed, fires attended and the fire exposure score, risks were mostly higher in the middle third, though not statistically significantly, and close to or below 1 in the highest third. For years in fire-exposed jobs and the inhalation score, estimates were close to 1. In the middle third of diesel exhaust exposure, risk was more than doubled with 10-year (incidence rate ratio 2.27, 95% CI 1.22 to 4.20) and 15-year (2.21, 1.18 to 4.16) lags, but close to 1 in the highest third. The authors concluded that no dose-response pattern was observed. They noted the small number of cases and the lack of smoking data. The study did not examine asbestos.

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: Cohort study with internal comparisons. Employment records were collected retrospectively and linked to national cancer, death and population registries. Poisson regression compared lowest, middle and highest thirds (tertiles) of cumulative exposure, with exposures lagged 0, 10 and 15 years.
• Who was studied: 4250 men employed at participating Norwegian fire departments (the Norwegian Fire Departments Cohort), followed for urinary tract cancer from 1 January 1960 to 31 December 2021. Women were excluded because there were few of them.
• Exposure: Firefighting exposure indicators built from work histories, fire statistics and department questionnaires: duration of employment, duration of fire-exposed employment, number of fires attended, fire exposure score, inhalation score (based on breathing apparatus use), and diesel exhaust exposure score at fire stations. Asbestos was not assessed.
• Main results:
  • There were 76 urinary tract cancer cases in the cohort. 64 were bladder cancers, 6 were of the renal pelvis, 4 of the ureter and 2 of the urethra and other urinary organs.
  • For total duration of employment, number of fires attended and fire exposure score, IRRs were mostly increased in the middle third, though not statistically significantly, and at or below 1 in the highest third, with and without lags.
  • Duration of employment, 15-year lag, age-adjusted model: the middle third had an IRR of 1.42 (95% CI 0.80 to 2.51) and the highest third had an IRR of 0.90 (0.46 to 1.77), both compared with the lowest third. Neither was statistically significant.
  • Number of fires attended, 15-year lag: the middle third had an IRR of 1.44 (0.76 to 2.70) and the highest third had an IRR of 0.58 (0.31 to 1.10). Neither was statistically significant. With no lag, the highest third had an IRR of 0.52 (0.28 to 0.95).
  • Duration of fire-exposed employment: IRRs were at or close to 1 in the middle and highest thirds.
  • Inhalation score: IRRs were close to 1 in the middle and highest thirds.
  • Diesel exhaust exposure score: the middle third had a more than twofold increased risk with a 10-year lag (IRR 2.27, 1.22 to 4.20) and with a 15-year lag (2.21, 1.18 to 4.16). IRRs were close to 1 in the highest third.
  • Findings restricted to bladder cancer were similar to those for all urinary tract cancers. Multivariable and sensitivity analyses also gave similar results.
• The authors' conclusion: The authors concluded that no dose-response associations were observed between the exposure indicators and urinary tract cancer, and that the study gave little support for elevated risk. They suggested diesel exhaust exposure may play a role in firefighters' urinary tract cancer risk, and called for future studies with more cases.
• Limitations the authors state:
  • There was no information on tobacco smoking, an important risk factor for urinary tract cancer.
  • Only 76 cases were observed, so the analyses had limited statistical power.
  • The fire statistics required extensive extrapolation, and no present or historical exposure measurements were available to build or check the indicators, so exposure may have been misclassified.
  • For the inhalation score, some exposure misclassification was likely, and exposure through other routes such as the skin was not captured.
  • The healthy worker survivor effect (less healthy workers leaving work earlier) may have lowered risk estimates at high exposures.

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Mesothelioma, Carcinogenic, Cancer Registry, Incidence, Cumulative Exposure, Dose-response relationship.

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