The incidence of thyroid cancer in the United States may be on decline since the rise in thyroid cancer diagnoses observed between 1974 and 2013. This finding is based on observational analysis of data from the Surveillance, Epidemiology, and End Results 13 registry, which were recently published in JAMA.<br />
Between 2009 and 2013, the subcentimeter thyroid cancer incidence began to stabilize at 4.7 to 5.3 per 100,000 annual percentage change (APC) 2.9%, (95% CI, −2.5% to 8.6%). The change in slope was t = −2.3 (P = .02). From 2013 to 2016, the incidence of thyroid cancer declined to 5.3 to 4.7 per 100,000 APC −3.7% (95% CI, −8.7% to 1.7%). The change in slope wast = −1.9, andP= .04. In the years prior, (2009-2013), the incidence of age-adjusted thyroid cancer was gradually increasing at 1.2 to 4.7 per 100,000. During that time, the greatest jump was APC 9.1% (95% CI, 8.4%-9.8%).
The study investigators have attributed the plateau from 2009 to 2013 and the decrease in the incidence of thyroid cancers from 2013 to 2016 to be predominantly due to changes in the detection of thyroid cancers, although they admit that other factors may have contributed to the new trend.
The study authors wrote, “These changes have occurred during a time of evolving understanding of overdiagnosis and the indolent nature of many small thyroid cancers, reflected in changing clinical practice guidelines, including recommendations against screening for thyroid cancer by the US Preventive Services Task Force (USPSTF) in 2017.”
The shift in clinical practice was due to new recommendations from the American Thyroid Association (ATA), regarding, initial evaluation, clinical and ultrasound criteria for fine-needle aspiration biopsy, interpretation of fine-needle aspiration biopsy results, use of molecular markers, and management of benign thyroid nodules. In terms of initial management, the ATA made new recommendations about screening for thyroid cancer, staging, and risk assessment, surgical management, radioiodine remnant ablation and therapy, and thyrotropin suppression therapy using levothyroxine (Synthroid). The long-term management recommendations were related to surveillance for recurrent disease using imaging and serum thyroglobulin, thyroid hormone therapy, management of recurrent and metastatic disease, and consideration for clinical trials and targeted therapy.2
The changes were also driven by recommendations from the USPSTF, which stamped detection of thyroid cancer in symptomatic adults as grade D, meaning they strongly recommend against it.3
The age-adjusted incidence of thyroid cancer seen from 1992 to 2016 in the SEER 13 registry was analyzed in 13 geographic regions which together represent 14% of the US. The analysis included all thyroid cancer histologies and stratified them by size, with reporting delay adjustment. By examining differences in slope between segments with a 1-tailed t-test, the investigators were able to asses changes in time series trends, at a threshold ofP< .05. The Weill Cornell Medicine institutional review board signed a data use agreement with the SEER program to conduct the study after they determined that the study was exempt from review and patient consent.
Other than the US, there have also been similar trends in the incidence of thyroid cancer observed in South Korea. The decline began in 2014 when new screening practices were implemented. This followed a large spike in thyroid cancer screenings leading to an increase in the incidence of thyroid cancer that was 15 times higher than what was observed 18 years prior.