Unravelling the rise in thyroid cancer incidence and addressing overdiagnosis.

The global incidence of thyroid cancer has risen sharply since the 1980s, whereas thyroid cancer mortality rates have remained relatively stable. Much of the increase in incidence can be attributed to overdiagnosis of small and indolent papillary thyroid cancers, which has largely been driven by widespread (and sometimes inappropriate) use of imaging studies, especially thyroid and neck ultrasonography. To a lesser extent, increases in the incidence rate of advanced-stage thyroid cancer over the past four decades have also contributed to the observed trends. This Review describes changes in the incidence of thyroid cancer over the past 40 years, outlines well-known and potential risk factors, including obesity and environmental exposures, and explores strategies to address the public-health issues of overdiagnosis and the consequent overtreatment of thyroid cancer.