Occupational class, occupational mobility and cancer incidence among middle-aged men and women: a prospective study of the French GAZEL cohort\*

Our plain-English summary of Occupational class, occupational mobility and cancer incidence among middle-aged men and women: a prospective study of the French GAZEL cohort*, by M. Melchior, M. Goldberg, N. Krieger, et al (Cancer Causes & Control, 2005).

The study

• Authors: M. Melchior, M. Goldberg, N. Krieger, I. Kawachi, G. Menvielle, M. Zins, L.F. Berkman
• Journal: Cancer Causes & Control
• Published: 2005;16(5):515-24
• Cited by: 34 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objective: To examine the association between occupational class, occupational mobility and cancer incidence in the 1990s.

Methods: Prospective study of 14,853 men and 5493 women employed by a large French company. Incident cases (any cancer, smoking and alcohol-related, breast) were ascertained through a validated company-based cancer registry (1990-2002). Hazard ratios (HRs) by occupational class and by career-long occupational mobility were calculated adjusting for age, marital status, tobacco and alcohol consumption, weight, diet, asbestos exposure, family history of cancer, and reproductive history.

Results: 359 male cancers (107 smoking and alcohol-related) and 208 female cases (120 breast cancers) were observed. Male clerks and manual workers were at high risk, particularly of smoking and alcohol-related cancers (compared to managers, age-adjusted HRs: 2.95 95% CI 1.37-6.38 and 2.18 95% CI 1.15-4.11). Adjusting for specific health behaviors and other cancer risk factors reduced this gradient (fully-adjusted HRs respectively 1.95 95% CI 0.89-4.27 and 1.54 95% CI 0.80-2.97). The risk was also associated with occupational mobility. We found no association between women's occupational class and cancer.

Conclusion: The incidence of smoking and alcohol-related cancers among French men shows a strong socioeconomic gradient. Policies addressing these social disparities are needed.

In plain English

This prospective cohort study followed 14,853 men and 5493 women employed by France's national gas and electricity company (EDF-GDF), all members of the GAZEL cohort who were cancer-free before 1990, through 2002. The authors examined whether occupational class in 1989 and job mobility over a career were associated with new cancer diagnoses. Men's occupational asbestos exposure, estimated with a job-exposure matrix, was one of the factors adjusted for. There were 359 cancers in men (107 smoking and alcohol-related) and 208 in women (120 breast). Compared with male managers, age-adjusted hazard ratios for smoking and alcohol-related cancers were 2.95 (95% CI 1.37–6.38) for clerks and 2.18 (95% CI 1.15–4.11) for manual workers. After adjustment for smoking, alcohol and other risk factors, these were 1.95 (0.89–4.27) and 1.54 (0.80–2.97), which were not statistically significant. No association was found between women's occupational class and cancer. The authors concluded that male clerks and manual workers had an increased risk of these cancers. They noted that cancer rates in the cohort were lower than in France as a whole, that few women were included, and that exposure to occupational carcinogens was rare.

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: prospective cohort study using a company-based cancer registry
• Who was studied: 14,853 men and 5493 women in the GAZEL cohort of employees of France's national gas and electricity company (EDF-GDF), aged 35 to 50 at enrolment in 1989, cancer-free before 1990, followed from 1990 to 2002
• Exposure: The main exposures were occupational class in 1989 (managers, associate professionals and technicians, office clerks, manual workers) and occupational mobility from hiring to 1989. Men's occupational asbestos exposure was estimated with a company job-exposure matrix (MATEX). It was used as an adjustment factor, with men classed as exposed or not exposed at a threshold of 5.75 fibers/cm3/year. No fiber type is named.
• Main results:
  • There were 359 incident cancers among men, 107 of them smoking and alcohol-related, and 208 among women, 120 of them breast cancers.
  • Compared with male managers, age-adjusted hazard ratios for smoking and alcohol-related cancers were 2.95 (95% CI 1.37–6.38) for male clerks and 2.18 (95% CI 1.15–4.11) for male manual workers.
  • After full adjustment (age, smoking, alcohol, marital status, body mass, fruit and vegetables, family history, occupational asbestos exposure), the hazard ratios for smoking and alcohol-related cancers were 1.95 (95% CI 0.89–4.27) for male clerks and 1.54 (95% CI 0.80–2.97) for male manual workers. The article states the hazard ratios fell by about 50% and were not statistically significant.
  • Men who stayed in intermediate or low grade jobs throughout their careers had an age-adjusted hazard ratio for smoking and alcohol-related cancers of 3.36 (95% CI 1.26–8.68), compared with men in stable high grade jobs. This was 2.15 (95% CI 0.81–5.72) after full adjustment.
  • Among women, occupational class was not associated with cancer. For example, the fully adjusted hazard ratio for all cancers in female clerks compared with managers was 1.03 (95% CI 0.59–1.80).
  • Among men, the hazard ratio associated with asbestos exposure above the threshold was 0.93 (95% CI 0.66–1.31) for all cancers in Table 2. The table does not clearly state which adjustments this figure includes.
• The authors' conclusion: The authors concluded that men who work as clerks and manual workers have an increased risk of incident smoking and alcohol-related cancer. In their view, cancer prevention efforts should focus on groups burdened by socioeconomic disadvantage.
• Limitations the authors state:
  • Men's cancer rates in the cohort were lower than in the French population, particularly for smoking and alcohol-related tumors.
  • Specific cancer sites could not be studied, so several smoking and alcohol-related cancers had to be grouped together.
  • With only 5493 women, the study had limited ability to detect socioeconomic gradients among women.
  • The cohort consisted of stably employed workers of one company, so severely disadvantaged or unemployed people were not studied and the external validity of the findings may be questioned.
  • Smoking and alcohol consumption were self-reported and measured at one point in time, and may have lacked precision.
  • Clerks' high risk may partly reflect reverse causation, meaning that less healthy individuals were selected into low grade jobs.
  • There were few manual workers in the cohort and exposure to occupational carcinogens was rare. The authors consider it likely that their results underestimate the contribution of occupational factors.

Topics

Medical terms in this study, explained in our Lexicon: Cancer Registry, Hazard Ratio, Asbestos Exposure.

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