Cancer incidence among Minnesota taconite mining industry workers

Our plain-English summary of Cancer incidence among Minnesota taconite mining industry workers, by E.M. Allen, B.H. Alexander, R.F. MacLehose, et al (Annals of Epidemiology, 2015).

The study

• Authors: E.M. Allen, B.H. Alexander, R.F. MacLehose, H.H. Nelson, G. Ramachandran, J.H. Mandel
• Journal: Annals of Epidemiology
• Published: 2015;25(11):811-5
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Purpose: To evaluate cancer incidence among Minnesota taconite mining workers.

Methods: We evaluated cancer incidence between 1988 and 2010 in a cohort of 40,720 Minnesota taconite mining workers used between 1937 and 1983. Standardized incidence ratios (SIRs) with 95% confidence intervals (CIs) were estimated by comparing numbers of incident cancers with frequencies in the Minnesota Cancer Surveillance System. SIRs for lung cancer by histologic subtypes were also estimated. We adjusted for out-of-state migration and conducted a probabilistic bias analysis for smoking-related cancers.

Results: A total of 5700 cancers were identified, including 51 mesotheliomas and 973 lung cancers. The SIRs for lung cancer and mesothelioma were 1.3 (95% CI = 1.2-1.4) and 2.4 (95% CI = 1.8-3.2), respectively. Stomach, laryngeal, and bladder cancers were also elevated. However, adjusting for potential confounding by smoking attenuated the estimates for lung (SIR = 1.1, 95% CI = 1.0-1.3), laryngeal (SIR = 1.2, 95% CI = 0.8-1.6), oral (SIR = 0.9, 95% CI = 0.7-1.2), and bladder cancers (SIR = 1.0, 95% CI = 0.8-1.1).

Conclusions: Taconite workers may have an increased risk for certain cancers. Lifestyle and work-related factors may play a role in elevated morbidity. The extent to which mining-related exposures contribute to disease burden is being investigated.

Copyright © 2015 Elsevier Inc. All rights reserved.

In plain English

This retrospective cohort study tracked new cancers from 1988 through 2010 among 40,720 Minnesota taconite (low-grade iron ore) mining industry workers, 93% of them men. The cohort also included people from earlier hematite mining operations. It compared the workers' cancer rates in the state cancer registry with Minnesota population rates. Taconite processing dust can contain nonasbestiform mineral particles and silica. The workers had 5700 cancers, including 973 lung cancers and 51 mesotheliomas. Mesothelioma occurred at 2.4 times the expected rate (95% confidence interval 1.8 to 3.2) and lung cancer at 1.3 times (1.2 to 1.4). Laryngeal, stomach and bladder cancers were also elevated. Lacking smoking data for the cohort, the authors statistically corrected using smoking rates from a 2010 survey of 1313 taconite workers. After this correction, the lung cancer figure was smaller but still elevated (1.1, 1.0 to 1.3), while laryngeal, oral and bladder cancers were close to what is expected in Minnesota. The authors concluded there was some evidence of higher risk for mesothelioma and other cancers, and that smoking and other unmeasured factors may explain some excesses.

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 cohort study of cancer incidence, comparing the workers' cancer rates with Minnesota population rates (standardized incidence ratios, SIRs), with a probabilistic bias analysis to adjust for smoking
• Who was studied: 40,720 Minnesota taconite mining industry workers (93% male, average 6.5 years worked). They were drawn from a database of 68,737 people who had ever worked in mines operating in 1983. That database included both taconite workers and people who had worked in earlier hematite mining operations. The cohort was limited to those born in 1920 or later and alive in 1988, and cancers were followed from 1988 through 2010.
• Exposure: Work in the taconite mining industry on the Mesabi Iron Range. Processing dust involves potential exposure to long and short nonasbestiform amphibole and nonamphibole elongate mineral particles (EMPs), respirable silica, and cleavage fragments.
• Main results:
  • 5700 cancers were identified among the 40,720 workers (5408 in men, 292 in women), including 973 lung cancers and 51 mesotheliomas.
  • Compared with the Minnesota population (adjusted for age, sex, calendar period and out-of-state migration), mesothelioma had an SIR of 2.4 (95% CI 1.8 to 3.2) and lung cancer had an SIR of 1.3 (95% CI 1.2 to 1.4).
  • Before smoking adjustment, laryngeal cancer (SIR 1.4, 95% CI 1.1 to 1.7), stomach cancer (SIR 1.4, 95% CI 1.1 to 1.6) and bladder cancer (SIR 1.1, 95% CI 1.0 to 1.2) were also elevated among the workers.
  • By lung cancer type, before smoking adjustment, SIRs were elevated for adenocarcinoma (SIR 1.2, 95% CI 1.1 to 1.4) and squamous cell carcinoma (SIR 1.3, 95% CI 1.2 to 1.5).
  • In the survey of 1313 current and former taconite workers, 38.2% were never smokers, compared with 50.1% of the reference population.
  • After adjustment for smoking, the workers' rates of laryngeal cancer (SIR 1.2, 95% CI 0.8 to 1.6), oral cancer (SIR 0.9, 95% CI 0.7 to 1.2) and bladder cancer (SIR 1.0, 95% CI 0.8 to 1.1) were similar to what is expected in Minnesota.
  • After adjustment for smoking, the lung cancer SIR among the workers was attenuated but still elevated (SIR 1.1, 95% CI 1.0 to 1.3).
  • After smoking adjustment, squamous cell and small cell lung carcinoma SIRs fell to about what would be expected in Minnesota. The text gives squamous SIR 1.1 (95% CI 0.9 to 1.2) and small cell SIR 0.9 (95% CI 0.8 to 1.1); Table 5 prints different figures (squamous 1.1, 0.9 to 1.3; small cell 1.0, 0.7 to 1.2).
  • Restricting the analysis to workers with at least 1 year of employment did not substantially change the results.
• The authors' conclusion: The authors concluded that the analysis provides some evidence that Minnesota taconite mining workers are at higher risk for mesothelioma and other cancers. They added that their sensitivity analysis indicates the elevated risk of some cancers may be a consequence of smoking and other unmeasured confounders.
• Limitations the authors state:
  • There was no information on the smoking habits of cohort members, and smoking is the major risk factor for lung cancer and many of the other cancers analyzed.
  • The registry captures only cancers diagnosed in Minnesota, so the person-years had to be adjusted for workers who moved out of state. This adjustment was estimated from out-of-state deaths.
  • Workers who died before 1988 were excluded, including 747 cancer deaths. Mesothelioma had no specific code before 1988 and could not be identified, so the SIRs could have been biased toward the null.
  • The smoking data came from a survey done in 2010, at the end of follow-up, and may not reflect past smoking habits.
  • Relying on survivors for smoking data risks underestimating the cohort's smoking prevalence.
  • The bias analysis could not examine an interaction with smoking.
  • Estimates of cancer rates in smokers versus nonsmokers vary among sources, although the authors report that changing this value did not substantially change the results.

Topics

Medical terms in this study, explained in our Lexicon: Taconite, Standardized Incidence Ratio (SIR), confidence interval, Lung Cancer, Histological Subtype, Mesothelioma, Confounding.

Related studies

• Mortality experience among Minnesota taconite mining industry workers — E.M. Allen, B.H. Alexander, et al. (2014)
• Occupational exposures and lung cancer risk among Minnesota taconite mining workers — E.M. Allen, B.H. Alexander, et al. (2015)
• Comprehensive assessment of exposures to elongate mineral particles in the taconite mining industry — J. Hwang, G. Ramachandran, et al. (2013)
• The relationship between various exposure metrics for elongate mineral particles (EMP) in the taconite mining and processing industry — J. Hwang, G. Ramachandran, et al. (2014)
• A case-control study of mesothelioma in Minnesota iron ore (taconite) miners — C.S. Lambert, B.H. Alexander, et al. (2016)
• The search for asbestos within the Peter Mitchell Taconite iron ore mine, near Babbitt, Minnesota — M. Ross, R.P. Nolan, et al. (2008)

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