Background: Thyroid cancer incidence has significantly increased in the United States over the past few decades. Recent studies have suggested a change in thyroid cancer incidence trends following 2013. The main objective of this study was to update the data on thyroid cancer incidence and mortality trends in the United States. Methods: Thyroid cancer incidence and incidence-based mortality trends were evaluated using the Surveillance, Epidemiology, and End Results-18 cancer registry. Cases of thyroid cancer diagnosed in 2000-2018 and thyroid cancer deaths during 2000-2018 were included. Annual percent change (APC) was calculated using joinpoint regression analysis. Results: Among 197,070 patients, female (75.6%) and white (81.0%) patients comprised the majority of cases. Papillary thyroid carcinoma (PTC) was the most common histology (89.1%). Incidence rates increased during 2000-2009 (APC 6.80, 95% confidence interval [CI 6.46 to 7.13]) and 2009-2014 (APC 2.58 [CI 1.71 to 3.47]) and then decreased during 2014-2018 (APC -2.33 [CI -3.15 to -1.51]). The incidence trends for PTC overall, localized disease, and tumors ≤1.0 cm mirrored the overall thyroid cancer trends, while incidence rates for regional disease stabilized during 2015-2018 (APC -1.65 [CI -4.09 to 0.84]). The incidence of distant disease decreased during 2015-2018 (APC -17.86 [CI -26.47 to -8.25]). The incidence of tumors ≤1.0 cm decreased (APC -5.83 [CI -7.24 to -4.40]), while the incidence of tumors 1.1-2.0 cm (APC -0.10 [CI -1.16 to 0.96]), 2.1-4.0 cm (APC 1.12 [CI -0.17 to 2.43]), and >4.0 cm (APC -1.13 [CI -4.58 to 2.45]) stabilized during the most recent 4-6 years. Incidence-based mortality increased throughout 2000-2018 (average APC 1.35 [CI 0.88 to 1.82]). Conclusions: Thyroid cancer incidence rates have declined since 2014. Similar declines are noted for PTC, localized disease, and tumors ≤1.0 cm, but not for tumors >2.0 cm. Incidence-based mortality rates continue to increase. These findings suggest that changing patterns in the management of thyroid nodules may have led to a decrease in diagnosis of small indolent tumors, but not more advanced tumors.

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