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Original research
Ongoing risk of bladder cancer among former workers at the last benzidine manufacturing facility in the USA
  1. Melissa L Millerick-May1,
  2. Ling Wang1,
  3. Carol Rice2,
  4. Kenneth D Rosenman1
  1. 1 Department of Medicine, Michigan State University, East Lansing, Michigan, USA
  2. 2 Department of Environmental & Public Health Sciences, University of Cincinnati, Cincinnati, Ohio, USA
  1. Correspondence to Dr Melissa L Millerick-May, Department of Medicine, Michigan State University, East Lansing, MI 48824, USA; milleric{at}


Objective To determine whether there is an ongoing risk of developing bladder cancer in a previously studied cohort of workers exposed to both benzidine and dichlorobenzidine or dichlorobenzidine only in the last benzidine manufacturing plant in the USA.

Methods Workers (n=488) were identified from the quarterly 941 forms the employer was required to submit to the Social Security Administration from 1960 to 1977. Exposures were assigned based on dates worked and known benzidine/dichlorobenzidine production schedules. Incidence, vital status and cause of death were determined through 2014. Analyses were restricted to white men.

Results Bladder cancer incidence and mortality were significantly increased (25 incident cases, standardised incidence ratio (SIR) 2.19, 95% CI 1.42 to 3.23, and 5 deaths, standardised mortality ratio (SMR) 3.79, 95% CI 1.23 to 8.84). There were significant increases in incidence and mortality in those exposed to both benzidine and dichlorobenzidine (SIR 3.11, 95% CI 1.97 to 4.67, SMR 4.10, 95% CI 1.12 to 10.50), but not among workers exposed to dichlorobenzidine only (two incident cases, SIR 0.89, 95% CI 0.11 to 3.23 and one death, SMR 2.90, 95% CI 0.07 to 16.15). Bladder cancer incidence and mortality were increased in individuals with >20 years since last exposure with >5 years worked (six observed, SIR 5.94, 95% CI 2.18 to 12.92 and two deaths, SMR 7.93, 95% CI 0.96 to 28.65).

Conclusions Incidence and mortality due to bladder cancer increased among workers exposed to benzidine but not among workers exposed only to dichlorobenzidine. The risk of incidence and death from bladder cancer remain elevated more than 20 years after last exposure to benzidine in those who worked >5 years.

  • cancer
  • retrospective exposure assessment

Data availability statement

No data are available. This is an ongoing study.

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Data availability statement

No data are available. This is an ongoing study.

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  • Contributors MLM-M, KDR and CR designed the study. MLM-M, LW and KDR analysed the data. MLM-M, LW, CR and KDR wrote, edited and revised the manuscript.

  • Funding This study was funded by the American Cancer Society (Award Number: MRSG-11-001-01-CPHPS).

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.

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