Importance: Thyroid cancer incidence has increased substantially in the United States over the last 4 decades, driven largely by increases in papillary thyroid cancer. It is unclear whether the increasing incidence of papillary thyroid cancer has been related to thyroid cancer mortality trends.
Objective: To compare trends in thyroid cancer incidence and mortality by tumor characteristics at diagnosis.
Design, setting, and participants: Trends in thyroid cancer incidence and incidence-based mortality rates were evaluated using data from the Surveillance, Epidemiology, and End Results-9 (SEER-9) cancer registry program, and annual percent change in rates was calculated using log-linear regression.
Exposure: Tumor characteristics.
Main outcomes and measures: Annual percent changes in age-adjusted thyroid cancer incidence and incidence-based mortality rates by histologic type and SEER stage for cases diagnosed during 1974-2013.
Results: Among 77 276 patients (mean [SD] age at diagnosis, 48 [16] years; 58 213 [75%] women) diagnosed with thyroid cancer from 1974-2013, papillary thyroid cancer was the most common histologic type (64 625 cases), and 2371 deaths from thyroid cancer occurred during 1994-2013. Thyroid cancer incidence increased, on average, 3.6% per year (95% CI, 3.2%-3.9%) during 1974-2013 (from 4.56 per 100 000 person-years in 1974-1977 to 14.42 per 100 000 person-years in 2010-2013), primarily related to increases in papillary thyroid cancer (annual percent change, 4.4% [95% CI, 4.0%-4.7%]). Papillary thyroid cancer incidence increased for all SEER stages at diagnosis (4.6% per year for localized, 4.3% per year for regional, 2.4% per year for distant, 1.8% per year for unknown). During 1994-2013, incidence-based mortality increased 1.1% per year (95% CI, 0.6%-1.6%) (from 0.40 per 100 000 person-years in 1994-1997 to 0.46 per 100 000 person-years in 2010-2013) overall and 2.9% per year (95% CI, 1.1%-4.7%) for SEER distant stage papillary thyroid cancer.
Conclusions and relevance: Among patients in the United States diagnosed with thyroid cancer from 1974-2013, the overall incidence of thyroid cancer increased 3% annually, with increases in the incidence rate and thyroid cancer mortality rate for advanced-stage papillary thyroid cancer. These findings are consistent with a true increase in the occurrence of thyroid cancer in the United States.