Estimating the incidence of lung cancer attributable to occupational exposure in Iran

Our plain-English summary of Estimating the incidence of lung cancer attributable to occupational exposure in Iran, by A. Mosavi-Jarrahi, M. Mohagheghi, B. Kalaghchi, et al (Population Health Metrics, 2009).

The study

• Authors: A. Mosavi-Jarrahi, M. Mohagheghi, B. Kalaghchi, Y. Mousavi-Jarrahi, M.K. Noori
• Journal: Population Health Metrics
• Published: 2009;7:7
• Cited by: 14 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objective: The aim of this study was to estimate the fraction of lung cancer incidence in Iran attributed to occupational exposures to the well-established lung cancer carcinogens, including silica, cadmium, nickel, arsenic, chromium, diesel fumes, beryllium, and asbestos.

Methods: Nationwide exposure to each of the mentioned carcinogens was estimated using workforce data from the Iranian population census of 1995, available from the International Labor Organization (ILO) website. The prevalence of exposure to carcinogens in each industry was estimated using exposure data from the CAREX (CARcinogen EXposure) database, an international occupational carcinogen information system kept and maintained by the European Union. The magnitude of the relative risk of lung cancer for each carcinogen was estimated from local and international literature. Using the Levin modified population attributable risk (incidence) fraction, lung cancer incidence (as estimated by the Tehran Population-Based Cancer Registry) attributable to workplace exposure to carcinogens was estimated.

Results: The total workforce in Iran according to the 1995 census identified 12,488,020 men and 677,469 women. Agriculture is the largest sector with 25% of the male and 0.27% of female workforce. After applying the CAREX exposure estimate to each sector, the proportion exposed to lung carcinogens was 0.08% for male workers and 0.02% for female workers. Estimating a relative risk of 1.9 (95% CI of 1.7-2.1) for high exposure and 1.3 (95% CI 1.2-1.4) for low exposure, and employing the Levin modified formula, the fraction of lung cancer attributed to carcinogens in the workplace was 1.5% (95% CI of 1.2-1.9) for females and 12% (95% CI of 10-15) for males. These fractions correspond to an estimated incidence of 1.3 and 0.08 cases of lung cancer per 100,000 population for males and females, respectively.

Conclusion: The incidence of lung cancer due to occupational exposure is low in Iran and, as in other countries, more lung cancer is due to occupational exposure among males than females.

In plain English

This modelling study estimated how much lung cancer in Iran was attributable to workplace exposure to eight established lung carcinogens, asbestos among them. The authors combined 1995 census workforce counts (12,488,020 men, 677,469 women) with CAREX exposure proportions drawn from Finnish and US workers. One weighted-average relative risk from published literature covered all eight carcinogens: 1.3 (95% CI 1.2 to 1.4) for low and 1.9 (95% CI 1.7 to 2.1) for high exposure. The article's body estimated that 8% of male and 2% of female workers were exposed. The estimated share of lung cancer due to these exposures was 12% (95% CI 10 to 15) in men and 1.5% (95% CI 1.2 to 1.9) in women, or 1.3 (1.1 to 1.6) cases per 100,000 males and 0.08 (0.06 to 0.09) among females. No separate asbestos estimate was given. The authors concluded that work-related lung cancer was moderate among males and very low among females, and called for validation with local exposure data. They noted CAREX may not fit Iran and the exposure split was arbitrary.

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: Population attributable fraction estimate (modelling study) combining census workforce data, CAREX exposure proportions, published relative risks and cancer registry incidence
• Who was studied: The Iranian workforce in the 1995 national census: 12,488,020 males and 677,469 females. Lung cancer rates came from the Tehran Population-Based Cancer Registry, which covers 10% of the Iranian population and was used to stand for the whole country.
• Exposure: Workplace exposure to eight lung carcinogens combined: silica, cadmium, nickel, arsenic, chromium, diesel fumes, beryllium and asbestos. There was no asbestos-specific analysis. A single mean relative risk of 1.6 was used for all eight. It was a weighted average of carcinogen-specific risks, partitioned into 1.3 (95% CI 1.2 to 1.4) for low-level and 1.9 (95% CI 1.7 to 2.1) for high-level exposure. Exposed workers were split 50/50 into low and high exposure.
• Main results:
  • In the body of the article, 8% of the male workforce and 2% of the female workforce were estimated to be exposed to the eight carcinogens. The abstract gives 0.08% and 0.02%.
  • The estimated fraction of lung cancer attributable to these workplace carcinogens was 12% (95% CI 10 to 15) among males and 1.5% (95% CI 1.2 to 1.9) among females. Table 2 gives 0.12 (0.10, 0.15) for males and 0.014 (0.011, 0.018) for females.
  • Estimated work-related lung cancer incidence was 1.3 (95% CI 1.1 to 1.6) per 100,000 population for males and 0.08 (95% CI 0.06 to 0.09) per 100,000 population for females.
• The authors' conclusion: The authors concluded that work-related lung cancer incidence in Iran was moderate among males and very low among females. They said further studies using locally obtained exposure data are needed to validate the estimate.
• Limitations the authors state:
  • CAREX exposure data come from Finland and the US, whose industries differ from Iran's. One example the authors give is that asbestos for construction materials was banned in Iran in early 1980.
  • The split between high and low exposure was chosen arbitrarily.
  • The partition factor used to divide exposed workers into low and high exposure is a source of uncertainty in the relative risks applied.
  • Local workforce data were converted to the international industry classification by expert review rather than at the point of data collection.
  • No official worker turnover rate exists for Iran, so a recommended default value of 4 was used.

Topics

Medical terms in this study, explained in our Lexicon: Lung Cancer, Occupational Exposure, Relative Risk, Population Attributable Fraction (PAF), Cancer Registry.

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