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

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.