Are rates of thyroid cancer among World Trade Center–exposed populations associated with medical surveillance?
In this cohort study of 14 987 male Fire Department of the City of New York rescue/recovery workers, the overall age-adjusted incidence rate of thyroid cancer among the Fire Department of the City of New York World Trade Center–exposed cohort was significantly greater than the rate among demographically similar, non–World Trade Center–exposed men. This difference may be explained by the high rate of asymptomatic cancers detected among individuals from the Fire Department of the City of New York; in addition, the Fire Department of the City of New York found no thyroid cancer–specific deaths or metastatic disease.
These findings suggest that increased rates of thyroid cancer in World Trade Center–exposed cohorts may be associated with heightened surveillance rather than an increase in disease.
Elevated incidence rates of thyroid cancer among World Trade Center (WTC)–exposed individuals may be associated with the identification of asymptomatic cancers during medical surveillance.
To examine the association between WTC exposure and thyroid cancer among Fire Department of the City of New York (hereafter, Fire Department) rescue/recovery workers as well as the association with medical surveillance.
Design, Setting, and Participants
This closed-cohort study classified the method of detection (asymptomatic and symptomatic) of thyroid cancers in 14 987 men monitored through the Fire Department–WTC Health Program diagnosed from September 12, 2001, to December 31, 2018. Age-, sex-, and histologic-specific Fire Department incidence rates were calculated and compared with demographically similar men in Olmsted County, Minnesota, from the Rochester Epidemiology Project using age-standardized rates, relative rates (RRs), and 95% CIs. The secondary analysis was restricted to papillary carcinomas.
World Trade Center exposure was defined as rescue/recovery work at the WTC site from September 11, 2001, to July 25, 2002.
Main Outcomes and Measures
The outcomes evaluated comprised (1) number of incident thyroid cancers and their detection method categorizations in the Fire Department and Rochester Epidemiology Project cohorts; (2) Fire Department, Rochester Epidemiology Project, and Surveillance, Epidemiology, and End Results-21 age-standardized incidence rates of thyroid cancer; and (3) RRs comparing Fire Department and Rochester Epidemiology Project overall and by detection method categorization.
Seventy-two post-9/11 Fire Department cases of thyroid cancer were identified. Among the 65 cases (90.3%) with a categorized detection method, 53 cases (81.5%) were asymptomatic and 12 cases (18.5%) were symptomatic. Median (interquartile range) age at diagnosis was 50.2 (44.0-58.6) vs 46.6 (43.9-52.9) years for asymptomatic vs symptomatic cases. Associated primarily with asymptomatic cancers, the overall age-standardized incidence of Fire Department thyroid cancers (24.7; 95% CI, 17.4-52.3) was significantly higher than the Rochester Epidemiology Project (10.4; 95% CI, 8.5-12.7) and Surveillance, Epidemiology, and End Results-21 (9.1; 95% CI, 9.0-9.1) per 100 000 person-years. Furthermore, the RR of thyroid cancer among symptomatic men in Fire Department cases was not significantly different from that of men in the Rochester Epidemiology Project (0.8; 95% CI, 0.4-1.5); however, the rate of asymptomatic cancers was more than 3-fold that of the Rochester Epidemiology Project rate (RR, 3.1; 95% CI, 2.1-4.7).
Conclusions and Relevance
Excess asymptomatic thyroid cancer in Fire Department WTC–exposed rescue/recovery workers is apparently attributable to the identification of occult lesions during medical surveillance. Among WTC-exposed cohorts and the general population, these findings appear to have important implications for how thyroid cancer incidence rates are interpreted and how diagnoses should be managed.
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Colbeth HL, Genere N, Hall CB, et al. Evaluation of Medical Surveillance and Incidence of Post-September 11, 2001, Thyroid Cancer in World Trade Center–Exposed Firefighters and Emergency Medical Service Workers. JAMA Intern Med. 2020;180(6):888–895. doi:10.1001/jamainternmed.2020.0950
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