Incidence of thyroid cancer in World Trade Center exposed firefighters

1. Fire Department World Trade Center-exposed workers demonstrate more asymptomatic thyroid cancers, attributable to occult lesion diagnoses, compared to non-WTC-exposed subjects of the Rochester Epidemiology Project and the general US population.

Evidence Rating Level: 2 (Good)

Incidence rates of thyroid cancer have increased by approximately 300% over the past 40 years, such that it is one of the most common forms of cancer diagnosed in the US. This increase is thought to be related to asymptomatic lesions, along with environmental exposures to harmful elements. This closed-cohort study examined the association between thyroid cancer and World Trade Center (WTC) exposure among rescue and recovery workers. These workers included 14,987 men from the Fire Department of the City of New York WTC-exposed cohort, with both asymptomatic (median [IQR] age at diagnosis = 50.2 [44.0 to 58.6] years) and symptomatic (median [IQR] age at diagnosis = 46.6 [43.9 to 52.9] years) detection methods of thyroid cancer. A total of 72 cases of thyroid cancer were detected, 65 of which had a categorized detection method and was used in further analyses. Approximately 81.5% were asymptomatic and 18.5% were symptomatic. Papillary thyroid cancer accounted for 98.1% of all cancers with a detection method and only one case of follicular carcinoma was found. Compared to the Rochester Epidemiology Project, the overall age-standardized incidence of thyroid cancer of those 20 years or older was greater in the Fire Department cohort (difference 14.3), which were accounted for by asymptomatic cancers. Post-9/11 thyroid cancer incidence among the Fire Department was double that of the Rochester Epidemiology Project (RR 2.3, 95% CI 1.7 to 3.2). While the relative rates of thyroid cancer in the Fire Department were not significantly different than those of the Rochester Epidemiology Project (RR 0.8, 95% CI 0.4 to 1.5), the rate of asymptomatic cancers among the Fire Department was three times greater than the Rochester Epidemiology Project (RR 3.1, 95% CI 2.1 to 4.7). Overall, this study suggests that thyroid cancer rates in WTC-exposed workers are higher than both non-WTC-exposed subjects of the Rochester Epidemiology Project as well as the US population but this difference may be secondary to increased surveillance. Limitations include the exclusion of women, lack of a non-WTC-exposed Fire Department group, and potential differential misclassification.

 Click to read the study in JAMA Internal Medicine

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