Examination of the Increase in Thyroid Cancer Incidence Among Younger Women in the United States by Age, Race, Geography, and Tumor Size, 1999-2007

Purpose: Thyroid cancer incidence has been increasing for several decades, but the reasons are not fully understood. Previous surveillance reports have covered less than 26% of the U.S. population. More recent, nationwide data are needed. This study examines thyroid cancer incidence among younger women by age, race/ethnicity, geography, and tumor size. Patients and Methods: Our study uses nationwide surveillance data to describe incidence rates and recent trends in thyroid cancer among adults aged 20-39 years in the United States during 1999-2007, with a focus on females. Results: Incidence rates were more than five times higher among females (16.4 per 100,000; 95% confidence interval [CI]: 16.2-16.6) than among males (3.1 per 100,000; 95% CI: 3.1-3.2). Among females, rates were higher among non-Hispanic whites than among other racial/ethnic groups and higher in the Northeast compared with other regions (p < 0.05). During 1999-2007, incidence rates increased 5.3% each year among females (95% CI: 4.7-5.9). This increase was observed across five-year age groups, racial/ethnic groups (except American Indians/Alaska Natives), geographic regions, and tumor sizes. Conclusion: The increase in rates across all tumor sizes suggests that the observed increases cannot be attributed solely to changes in diagnostics or surveillance. In addition, the continued increase in incidence rates in recent years among persons born after 1960 suggests that other, more contemporary factors than those previously proposed may play a contributing role.