High thyroid cancer rate among 9/11 responders likely due to heightened surveillance
An increased rate of thyroid cancers observed among firefighters who responded to the 9/11 World Trade Center attack may be associated with heightened surveillance rather than an increase in disease, according to findings published in JAMA Internal Medicine.
“The results of our study indicate that the high rate of thyroid cancers detected among Fire Department of the City of New York World Trade Center (WTC)-exposed rescue/recovery workers may be primarily attributable to the heightened medical surveillance they experience as compared with demographically similar non-WTC-exposed men and the general male population,” Rachel Zeig-Owens, DrPH, lead epidemiologist at the WTC Health Program Fire Department of the City of New York and research assistant professor, epidemiology and population health, at Albert Einstein College of Medicine, told Healio.
In a closed-cohort study, Zeig-Owens and colleagues analyzed data from 14,987 men who arrived at the WTC site to assist with rescue and recovery efforts between the morning of Sept. 11, 2001, and July 25, 2002 (88% white; duration of work at the site ranged from 1 to 10 months). Women were excluded due to the small sample size. Researchers identified confirmed thyroid cancer cases diagnosed between Sept. 12, 2001, and Dec. 31, 2018, and classified cases as asymptomatic or symptomatic. Demographic data and medical testing history before the diagnosis date were collected from the WTC Health Program records. Researchers calculated age-, sex- and histologic-specific fire department incidence rates and compared those rates with a reference cohort of demographically similar men living in Olmsted County, Minnesota (the Rochester Epidemiology Project; 90.3% white) during a similar period (2000-2018). Age-standardized incidence was calculated as the number of confirmed cases per 100,000 person-years. Researchers used Poisson regression models for grouped data to estimate relative rates for thyroid cancer.
Symptomatic vs. asymptomatic detection
Between Sept. 12, 2001, and Dec. 31, 2018, researchers identified 72 cases of thyroid cancer among fire department workers, with 65 (90.3%) categorized with a detection method. Among categorized cases, 53 cases (81.5%) were asymptomatic and 12 cases (18.5%) were symptomatic. Median age at diagnosis was 50 years for asymptomatic men and 47 years for symptomatic men; median time to diagnosis was 11.5 years after Sept. 11, 2001. No firefighters died of thyroid cancer and none developed metastatic disease (98.1% papillary cancers). Within the Rochester Epidemiology Project cohort, researchers identified 54 asymptomatic cancer cases and 45 symptomatic cancer cases. Median age at diagnosis was 50 years, with 92.9% of cases papillary thyroid cancers.
The overall age-standardized incidence of thyroid cancer among men aged at least 20 years was higher among New York firefighters vs. men participating in the Rochester Epidemiology Project (24.7 vs. 10.4 per 100,000 person-years), and was also higher compared with men in the Surveillance, Epidemiology and End Results-21 (SEER-21) cancer registry (9.1 per 100,000 person-years).
“Asymptomatic cancers accounted for this difference,” the researchers wrote.
Researchers found that, by detection method, the thyroid cancer rate among symptomatic fire department cases did not differ from men participating in the Rochester Epidemiology Project cases (RR = 0.8; 95% CI, 0.4-1.5); however, researchers observed three times as many asymptomatic cancers among fire department workers vs. Rochester Epidemiology Project cases (RR = 3.1; 95% CI, 2.1-4.7).
“The American Thyroid Association recommends a management approach of active surveillance as a safe and effective alternative to immediate surgery in patients with very low-risk tumors such as papillary microcarcinomas without clinically evident metastases or local invasion, and no cytologic evidence of aggressive disease,” Zeig-Owens said. “This protocol could be adopted for many World Trade Center-exposed patients with qualifying low-risk carcinomas.”
Screenings ‘not beneficial’
In commentary accompanying the study, H. Gilbert Welch, MD, MPH, of the Center for Surgery and Public Health in Boston, wrote that the excess thyroid cancer observed among New York first responders after Sept. 11 appear to be the result of incidental detection rather than screening.
“There is no evidence that thyroid cancer screening or incidental detection is beneficial for anyone,” Welch wrote. “In fact, I would argue that there is good evidence that it does not: Despite all of the additional detection, thyroid cancer mortality remains the same. But it is hard to stop this train, and once ‘cancer’ is diagnosed, the train has already left the station.”
Zeig-Owens said research is needed to examine the decision-making process and acceptability of an active surveillance approach to thyroid cancer among WTC-exposed patients and their clinicians. – by Regina Schaffer
For more information:
Rachel Zeig-Owens, DrPH, can be reached at the Fire Department of the City of New York, Bureau of Health Statistics, FDNY Headquarters, 9 Metrotech Center, Brooklyn, NY 11201; email: Rachel.zeig-owens@fdny.nyc.gov.
Disclosures: The authors report no relevant financial disclosures. Welch reports no relevant financial disclosures.
Perspective
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This study assesses whether surveillance bias is partly responsible for the observed increased risk for thyroid cancer among the firefighters who responded to the World Trade Center attack in 2001.
Surveillance bias occurs when a group — in our case, the World Trade Center first responders — is more likely to have a disease detected than another group or the general population because of increased screening. In the case of thyroid cancer, we know that the large number of respiratory health issues responders developed has prompted a higher rate of diagnostic chest imaging. This could explain increased thyroid cancer diagnoses. If this is the case, we would expect these tumors to be detected when they are smaller or in early stages and when patients are younger.
The current study uses the rate of asymptomatic diagnoses as an indirect marker for cancers that were detected by surveillance and shows that the rate of asymptomatic thyroid cancers in the responder cohort is significantly higher than in a comparison cohort, the Rochester Epidemiology Project. Asymptomatic cases were also diagnosed at a younger age vs. symptomatic cases. Unfortunately, there was no information on tumor size and stage at diagnosis, something that would have strengthened the hypothesis that surveillance bias is involved in the observed increase in thyroid cancer among the responder cohort.
Another limitation of this study, which is also a general limitation of studies of World Trade Center responders, is that there is no perfect cohort that can be used as comparison, as the authors mention in the limitation section of their paper.
Future studies should focus on markers of aggressiveness in World Trade Center responders’ thyroid cancers compared with non-responder cases.
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