A bump in thyroid cancer rates among male fire personnel who responded to the aftermath of 9/11 at the World Trade Center (WTC) may be linked with heightened surveillance rather than an increase in disease, researchers reported.
In a closed-cohort study (n=14,987), in which WTC exposure was defined as rescue/recovery work at the site from Sept. 11, 2001 to July 25, 2002, 72 cases of thyroid cancer were identified among members of the post-9/11 Fire Department of the City of New York. Among the 65 cases (90.3%) with a categorized detection method, 81.5% were asymptomatic and 18.5% were symptomatic, according to Rachel Zeig-Owens, DrPH, MPH, of the Fire Department of the City of New York, Bureau of Health Services, FDNY Headquarters, in New York City, and co-authors.
They found that for asymptomatic thyroid cancers, the overall age-standardized incidence in this cohort was significantly higher than the Rochester Epidemiology Project (REP) and Surveillance, Epidemiology, and End Results-21 per 100,000 person-years at 24.7 (95% CI 17.4-52.3) versus 10.4 (95% CI 8.5-12.7) and 9.1 (95% CI 9.0-9.1).
Also, the relative rates of thyroid cancer among symptomatic men in fire department cases was not significantly different from that of men in REP (0.8, 95% CI 0.4-1.5, but the rate of asymptomatic cancers was more than three-fold that of the REP rate (RR 3.1, 95% CI 2.1 to 4.7), they wrote in JAMA Internal Medicine.
“The high incidence of thyroid cancer post-9/11 appears to be attributable to the increased diagnosis of occult lesions owing to the detailed and frequent medical testing of WTC-exposed individuals,” Zeig-Owens’ group concluded. “There seems to be no incidence of disease-specific thyroid cancer mortality, and carcinoma discoveries were largely of the least-aggressive subtypes, suggesting that the observed RRs are due to a greater detection of subclinical cancers in Fire Department rescue/recovery workers than in the comparison population.”
They added that their findings have “important implications for how thyroid cancer incidence rates are interpreted and how cases should be managed once diagnosed… for the general population.”
In an invited commentary accompanying the study, H. Gilbert Welch, MD, MPH, of the Center for Surgery and Public Health in Boston, stressed that “There is no evidence that thyroid cancer screening or incidental detection is beneficial for anyone…Screening is a purposeful act; however, incidental detection is inadvertent.”
Welch suggested the “radical” idea of “[masking] the thyroid out of CT and magnetic resonance images? Unless a thyroid image is specifically requested by the ordering physician, blank it out of the image. Not only would this procedure save time for radiologists, it would save thyroids for patients. Plus, it would focus radiologists on the question at hand that, for World Trade Center rescue and recovery workers at least, revolves around the lung parenchyma.”
He added that this strategy of “hiding clinical data” would “reduce unwanted extraneous data [which] can “both obscure and distract from the important aspects of a patient’s condition. More importantly, they can also create anxiety for both patients and clinicians, triggering further diagnostic testing and adverse effects of excessive intervention.”
The authors explained that previous research – including a study by Welch and colleague – has concluded that the increasing incidence of thyroid cancer can be tied to better diagnostic imaging that pinpoints incidental, small, asymptomatic lesions, although other studies question that association.
“Studies proposing an increase in incidence often attribute the increase to environmental exposures, such as atmospheric or medical radiation therapy, or to excess body mass,” they wrote. “The large quantity and variety of toxicants released into the environment following the [WTC] terrorist attacks on [9/11] may represent an environmental exposure contributing to the 2- to 3-fold greater risk of thyroid cancer among WTC-exposed populations compared with the general population.”
For their study, they classified the method of detection for both asymptomatic and symptomatic thyroid cancers in 14,987 men monitored through the Fire Department-WTC Health Program, and who were diagnosed from Sept. 12, 2001, to Dec. 31, 2018. Age-specific sex-specific, and histologic-specific fire department incidence rates were calculated and compared with demographically similar men from the REP. The secondary analysis was limited to papillary carcinomas.
Zeig-Owens and co-authors reported that median age at diagnosis was 50 years and the median time to diagnosis was 11.5 years post-9/11. The demographics, such as age and BMI, of those with and without thyroid cancer were largely similar, but men without thyroid cancer had a slightly higher proportion of ever-smokers (37.0% versus 26.4%). Almost 53% were known to have had unrelated medical testing before the thyroid cancer diagnosis, they added.
Compared with symptomatic cases, asymptomatic cases were white (88.7% versus 83.3%), firefighters (94.3% versus 88.3%), and ever-smokers (28.3% versus 16.7%). Papillary thyroid cancer accounted for 98.1% of fire department cancers with a detection method, with a single case of follicular carcinoma.
Overall, 57% of cases identified with a detection method had unrelated medical testing before the thyroid cancer diagnosis, and “The proportion of patients with asymptomatic cases known to have had unrelated medical testing (62.3%) was almost twice that of those with symptomatic cases (33.3%),” the authors stated.
Ultimately, none of the one of the monitored men with thyroid cancer experienced thyroid cancer-specific mortality and none developed metastatic disease, they reported.
The authors pointed out that there was no significant difference in the fire department thyroid cancer incidence versus REP incidence during the early post-9/11 period. During the late period (2010-2018), when access to medical care increased with the passage of the James L. Zadroga 9/11 Health and Compensation Act, fire department incidence increased to 2.5 times that of REP.
“Given that detection of subclinical pools of thyroid cancer lesions can be directly related to health care access, we believe that the totality of our results suggests that incidental detection has played a role in the elevated incidence of WTC-exposed thyroid cancers reported by previous studies,” Zeig-Owens’ group wrote.
Study limitations included the lack of a comparison group of fire department personnel who were not exposed to the WTC and the exclusively male, white cohort who had “above-average physical health prior to WTC exposure,” which does limit the general application of the findings.
However, Welch noted the findings do have more general, practical application: “A good place to begin to reduce extraneous data is in radiology, where the problem of incidental detection goes well beyond the thyroid. Clinicians ordering abdominal CTs frequently receive recommendations to follow up incidental findings in the chest. Conversely, clinicians ordering chest CTs receive recommendations for following up incidental findings in the abdomen. Such cross-diaphragmatic findings are unintended; the ordering clinician did not request information about the other side of the diaphragm. To deal with the problem of incidental detection, blanking out such unwanted data is the obvious place to start.”
The overall age-adjusted incidence rate of thyroid cancer among male Fire Department of the City of New York rescue/recovery workers with exposure to the post-9/11 World Trade Center (WTC) was significantly greater than the rate among demographically similar, non-WTC-exposed men, and the difference may be explained by the high rate of asymptomatic cancers detected in the study cohort of fire personnel.
The findings suggest that increased rates of thyroid cancer in WTC–exposed cohorts may be associated with heightened surveillance rather than an increase in disease.
Shalmali Pal, Contributing Writer, BreakingMED™
The study was supported by the National Institute for Occupational Safety and Health (NIOSH).
Zeig-Owens reported grants from NIOSH. Co-authors reported support from NIOSH, the National Cancer Institute, the University of California Davis, Johns Hopkins University, the National Institute of Aging, the NIH, the University of Iowa, and Washington University.
Welch reported no relationships relevant to the contents of this paper to disclose.
Cat ID: 120
Topic ID: 78,120,730,110,120,192,925