Increased rates of thyroid cancer among World Trade Center (WTC)-exposed firefighters and emergency medical service personnel who participated in rescue/recovery efforts after 9/11 are likely due to medical surveillance rather than an actual increase in disease.
This is the conclusion of a recently published study in JAMA Internal Medicine (https://jamanetwork.com/journals/jamainternalmedicine/article-abstract/2764101) in which investigators found excess asymptomatic thyroid cancer in these WTC-exposed personnel compared to a demographically similar non-WTC exposed cohort, but no differences in thyroid cancer-specific deaths or metastatic disease.
The study included 14,987 male WTC-exposed firefighters and emergency medical service personnel (women were excluded because of their small sample size) monitored through a medical surveillance program.
Between Sept. 12, 2001, and Dec. 31, 2018, 72 men were diagnosed with thyroid cancer, of which 65 (90.3%) could be categorized as asymptomatic (n=53; 81.5%) or symptomatic (n=12; 18.5%). Median age at diagnosis was 50.2 years and 46.6 years, respectively, and the median time to diagnosis was 11.5 years after Sept. 11, 2001. None of the men had thyroid cancer-specific mortality or metastatic disease.
To evaluate the association between WTC exposure and thyroid cancer among these workers, the investigators compared the incidence of thyroid cancer to a cohort of demographically similar men from the Rochester Epidemiology Project (REP) during a similar time period. In this cohort, 99 men were diagnosed with thyroid cancer. Among these, 54 (54%) were asymptomatic and 45 (45.5%) were symptomatic.
When assessing age-standardized incidence rates between the two cohorts, asymptomatic cancers were significantly higher in the WTC cohort (24.7; 95% CI, 17.4-52.3) compared to the REP cohort (10.4; 95% CI, 8.5-12.7) and Surveillance, Epidemiology, and End Results (SEER)-21 (9.1; 95% CI, 9.0-9.1) per 100,000 person-years.
Overall, men in the WTC cohort had a three-fold rate of asymptomatic cancers compared to the REP cohort (relative rate [RR], 3.1; 95% CI, 2.1-4.7). No significant difference between the two cohorts was found in the RR of thyroid cancer among symptomatic men (0.8; 95% CI, 0.4-1.5).
“Our results have important implications for how thyroid cancer incidence rates are interpreted and how cases should be managed once diagnosed, not only for WTC-exposed cohorts, but for the general population as well,” conclude the investigators.