Cancer risks in a historical UK cohort of benzene exposed workers

Our plain-English summary of Cancer risks in a historical UK cohort of benzene exposed workers, by T. Sorahan, L.J. Kinlen, R. Doll (Occupational and Environmental Medicine, 2005).

The study

• Authors: T. Sorahan, L.J. Kinlen, R. Doll
• Journal: Occupational and Environmental Medicine
• Published: 2005;62(4):231-6
• Cited by: 69 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Aims: To examine mortality from different causes and cancer incidence among a cohort of benzene workers in England and Wales.

Methods: A cohort of 5514 workers who had been occupationally exposed to benzene in 1966/67 or earlier was assembled by the former Factory Inspectorate and the Medical Research Council from details provided by 233 employers in England and Wales. The cohort was followed up for mortality (1968-2002) and cancer registrations (1971-2001). National mortality rates and cancer registration (incidence) rates were used to calculate standardised mortality ratios and standardised registration ratios.

Results: Mortality was close to expectation for all causes and significantly increased for cancer of the lip, cancer of the lung and bronchus, secondary and unspecified cancers, acute non-lymphocytic leukaemia (ANLL), and all neoplasms. Significant deficits were shown for three non-malignant categories (mental disorders, diseases of the digestive system, accidents). SMRs for other leukaemia, lymphomas, and multiple myeloma were close to or below expectation. There was some evidence of under-ascertainment of cancer registrations, although significantly increased SRRs were shown for lung cancer and cancer of the pleura (mesothelioma).

Conclusions: Many study subjects would have been exposed to carcinogens other than benzene (for example, asbestos, rubber industry fumes, foundry fumes, polycyclic aromatic hydrocarbons), and the excesses of lung cancer and mesothelioma are likely to reflect exposures to these other carcinogens. The carcinogenic effects of benzene exposure on the lymphohaematopoietic system were limited to ANLL.

In plain English

This historical cohort study followed 5514 workers from 233 firms in England and Wales who were exposed to benzene at work in 1966/67 or earlier. The authors compared deaths (1968–2002) and cancer registrations (1971–2001) with national rates; a ratio of 100 equals the expected number. Overall mortality was close to expectation (SMR 101, 2430 deaths). Lung cancer deaths were increased (SMR 121, 294 deaths), as were deaths from acute non-lymphocytic leukaemia (ANLL) (SMR 183, 14 deaths). Pleural cancer registrations were increased (SRR 237, 95% CI 133 to 391, 15 cases). Among workers making chemicals and dyes, the pleural cancer excess was significant (SRR 536, 9 cases). The article did not show the other sectors' figures, and the sector ratios did not differ significantly. Only six of the 15 cases had pleural cancer recorded as the underlying cause of death. The authors noted that asbestos was used in some of the factories. They concluded there was no reason to suspect that benzene caused the lung and pleural cancer increases. They attributed the ANLL increase to benzene, though a role for other unrecognised leukaemogens could not be excluded. Limitations they stated included missed cancer registrations and no individual exposure estimates.

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: historical (retrospective) cohort study comparing observed deaths and cancer registrations with national rates (standardised mortality ratios and standardised registration ratios)
• Who was studied: 5514 workers (5130 men, 384 women) exposed to benzene at work in 1966/67 or earlier, reported by 233 firms or plants in England and Wales; mortality followed 1968–2002 and cancer registrations 1971–2001
• Exposure: Occupational benzene exposure in industries including coking plants, chemicals and dyes, rubber, printing, paint, foundries and oil refining. Facility-level benzene estimates referred to 1966/67 and were available for only 130 of the 233 facilities. Workers were also exposed to other carcinogens, and asbestos is known to have been used in some of the factories.
• Main results:
  • In the whole cohort, mortality from all causes was close to expectation: SMR 101, based on 2430 deaths
  • In the whole cohort, lung cancer mortality was significantly increased: SMR 121 (95% CI 107 to 135), based on 294 deaths
  • In the whole cohort, mortality from acute non-lymphocytic leukaemia was significantly increased: SMR 183 (95% CI 100 to 307), based on 14 deaths (12 acute myeloid leukaemia, two acute leukaemia of unspecified cell type)
  • In the cancer incidence analysis, registrations were significantly increased for lung cancer (SRR 119, 95% CI 106 to 134, 293 cases) and for pleural cancer (SRR 237, 95% CI 133 to 391, 15 cases)
  • Deaths with pleural cancer as the underlying cause numbered 7, against 3.5 expected: SMR 202 (95% CI 81 to 415)
  • All 15 workers diagnosed with pleural cancer had died, but only six had pleural cancer as the underlying cause of death. Three deaths from 'mesothelioma of the lung' were coded to lung cancer, five from 'malignant mesothelioma' were coded to unspecified cancer, and one was a suicide.
  • By industry sector, there was no significant heterogeneity in pleural cancer SRRs, and the other sectors' figures were not shown. Among employees in the manufacture of chemicals and dyes, there was a significant excess: SRR 536, based on 9 cases (p less than 0.001).
  • Incidence of non-Hodgkin's lymphoma (SRR 100, 24 cases) and of leukaemia overall (SRR 120, 25 cases) was unremarkable. Mortality from all leukaemia excluding ANLL was SMR 95, based on 8 deaths.
  • The authors attributed the increased ANLL risk to benzene exposure, while stating that some role for other unrecognised leukaemogens could not be excluded
• The authors' conclusion: The authors concluded there was no reason to suspect that benzene was responsible for the increased lung and pleural cancer risks. They pointed to other carcinogens, including asbestos, used in some factories. They also concluded the study does not support claims that benzene affects risks for blood and lymph cancers other than ANLL.
• Limitations the authors state:
  • Some cancer registrations were very likely missed
  • Estimates of earlier benzene exposure for individual workers were not available, and the 1966/67 estimates were not provided in a standardised way
  • The industry-sector analyses had small numbers of leukaemia deaths
  • Job titles were not recorded
  • Unexposed workers at the same facilities were not enrolled for comparison
  • Some certifying doctors were probably unaware of how their wording on deaths that were almost certainly pleural mesothelioma would be coded for national mortality statistics

Topics

Medical terms in this study, explained in our Lexicon: Bronchus, Neoplasm, Myeloma, Lung Cancer, Pleura, Mesothelioma, Carcinogenic.

Related studies

• Risk of cancer among Danish utility workers--a nationwide cohort study — C. Johansen, J.H. Olsen (1998)
• Cancer incidence in a chlorochemical plant in Isère, France: an occupational cohort study, 1979-2002 — V. Bonneterre, G. Mathern, et al. (2012)
• An analysis of violations of Osha's (1987) occupational exposure to benzene standard — P.R. Williams (2014)
• Mortality and cancer morbidity in a cohort of Canadian petroleum workers — R.J. Lewis, A.R. Schnatter, et al. (2003)
• Historical cohort study of US man-made vitreous fiber production workers: I. 1992 fiberglass cohort follow-up: initial findings — G.M. Marsh, A.O. Youk, et al. (2001)
• Historical cohort study of US man-made vitreous fiber production workers: II. Mortality from mesothelioma — G.M. Marsh, M.J. Gula, et al. (2001)

Browse more research in Occupational and Environmental Medicine, or return to medical research.