Attributable fraction and number of cancer cases attributed to occupational carcinogens in Iran in 2019

Our plain-English summary of Attributable fraction and number of cancer cases attributed to occupational carcinogens in Iran in 2019, by A. Naghibzadeh-Tahami, Y. Khosravi, A.R. Zamani, et al (BMC Public Health, 2026).

The study

• Authors: A. Naghibzadeh-Tahami, Y. Khosravi, A.R. Zamani, A.A. Haghdoost
• Journal: BMC Public Health
• Published: 2026;26(1)
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Although occupational exposure to carcinogenic agents accounts for only a relatively small fraction of cancers, the estimated burden in Iran remains considerable due to widespread exposure in major industries and the scarcity of national data. This study aimed to estimate the proportion and number of cases of bladder, leukemia, lung, laryngeal, and liver cancers attributable to four major occupational carcinogens-silica, benzene, asbestos, and lead-in Iran in 2019.

Methods: An attributable fraction (AF)-based approach was used to estimate the burden of occupational cancers in Iran. AFs were calculated using odds ratios (ORs) associated with specific occupational exposures. Although AFs are traditionally calculated using relative risks (RRs), ORs were used because they are more commonly reported in occupational studies and can approximate RRs when outcomes are rare. For each exposure, ORs were selected from epidemiological sources, including industry- or population-based studies, meta-analyses, and reviews. The number of workers exposed to occupational carcinogens in 2019 was obtained from the national occupational exposure surveillance system. AFs were then applied to national cancer incidence data to estimate the attributable numbers (ANs) of cancers related to occupational exposures. Monte Carlo simulation was used to estimate uncertainty intervals (UIs) for both AFs and ANs.

Results: In 2019, 60 (95% UI: 46-77) cases of lung, bladder, liver, laryngeal, and leukemia cancers were attributable to historical lead exposure (AF = 34%). The total number of cancer cases attributable to historical silica exposure was estimated at 623 (95% UI: 365-881) (AF = 36%). Furthermore, 602 (95% UI: 334-887) cases of bladder, lung, liver, leukemia, and laryngeal cancers were attributable to occupational benzene exposure (AF = 23%). For asbestos, the AF was 42%, but the estimated attributable number was very small because of the limited number of exposed workers (AN = 0.41, 95% UI: 0.264-0.538).

Conclusion: These findings suggest that occupational exposure to carcinogenic agents may contribute substantially to the burden of selected cancers in Iran. Although the estimates are exploratory and based on scenario-based modeling assumptions, they highlight the importance of preventive workplace interventions and improved occupational exposure surveillance systems.

© 2026. The Author(s).

In plain English

This modelling study estimated cancers in Iran attributable to four workplace carcinogens: silica, benzene, asbestos and lead. The article calls them 2019 estimates, but the model assumed 40 years of exposure and describes the combined total as covering 40 years. The cancers were lung, bladder, laryngeal and liver cancer and leukemia, not mesothelioma. Odds ratios from published studies, mostly international, were combined with national cancer registry rates and Ministry of Health counts of exposed workers. Among exposed workers, the asbestos attributable fraction across the five cancers was 42% (95% uncertainty interval 18 to 60). Only 57 workers were reported as asbestos-exposed, so asbestos-attributable cases were estimated at about 0.41 (0.264 to 0.538). The model attributed 623 cases (365 to 881) to silica, 602 (334 to 887) to benzene and 60 (46 to 77) to lead. Together these totalled 1,285 cases over 40 years, or 2,571 assuming only 50% of occupational exposure was reported. The authors called the estimates exploratory, not precise, noting exposure levels were not measured. They concluded that historical workplace exposures may contribute meaningfully to Iran's cancer burden.

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: Scenario-based modelling study estimating attributable fractions and attributable numbers of cancers. It used odds ratios taken from a systematic review of published studies, with Monte Carlo simulation for uncertainty intervals.
• Who was studied: Workers in Iran recorded in the Ministry of Health's national occupational exposure surveillance system in 2019 (196,854 workers exposed to chemical carcinogens), combined with 2019 Iranian National Cancer Registry incidence for lung, bladder, laryngeal and liver cancer and leukemia
• Exposure: Occupational exposure to silica, benzene, asbestos and lead, with workers assumed to be exposed for an average of 40 years. Odds ratios for asbestos came from six published studies; the asbestos fiber type is not specified.
• Main results:
  • Asbestos: the attributable fraction across the five cancers (lung, bladder, liver, larynx, leukemia) was 42% (95% UI 18 to 60). Attributable fractions are expressed for cancer cases among workers in Iranian industries.
  • Asbestos: total attributable number about 0.41 cases (95% UI 0.264 to 0.538), because only 57 workers were reported to be exposed
  • Silica: an estimated 623 (95% UI 365 to 881) cases of the five cancers were attributed to historical silica exposure (attributable fraction 36%)
  • Benzene: an estimated 602 (95% UI 334 to 887) cases were attributed to historical benzene exposure (attributable fraction 23%)
  • Lead: an estimated 60 (95% UI 46 to 77) cases were attributed to historical lead exposure (attributable fraction 34%)
  • All four exposures combined, over a 40-year period: an estimated 1,285 attributable cases assuming 100% reporting in the occupational exposure surveillance system
  • Under a hypothetical scenario assuming 50% under-reporting of occupational exposure, the combined total rose to 2,571 cases
• The authors' conclusion: The authors concluded that historical workplace exposures to carcinogens may contribute meaningfully to Iran's cancer burden. They said the estimates are preliminary and should be interpreted cautiously.
• Limitations the authors state:
  • Only four carcinogens were recorded in the national surveillance system; other established or probable carcinogens were not included
  • Exposure levels were not directly measured, and the true prevalence and intensity of exposure are uncertain
  • The model assumed no confounding or interaction effects, a fixed population structure and linear exposure-response relationships
  • Effect estimates came largely from studies in developed countries and may not reflect conditions in Iran
  • The uncertainty intervals reflect only variability in the model inputs, not full epidemiological uncertainty

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Carcinogenic, Odds Ratio, Relative Risk, Laryngeal Cancer.

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