Investigators from the National Cancer Institute, Division of Cancer Epidemiology and Genetics (DCEG), and Duke University Medical Center evaluated long-term trends in thyroid cancer incidence and mortality according to histology, stage, and tumor size at diagnosis. Using data from the SEER-9 cancer registries, they identified 77,276 cases of thyroid cancer diagnosed between 1974 and 2013, of whom 2,371 died of thyroid cancer between 1994 and 2013. They found that overall incidence of thyroid cancer increased more than threefold over the past four decades, by an average of 3.6% per year, mainly driven by an increase (4.4% per year) in papillary thyroid cancer (PTC), the most common type. Thyroid cancer mortality rates increased by an average of 1.1% per year over the past two decades, with the greatest increase (1.7% per year) observed for patients diagnosed with PTC. For advanced-stage PTC, average yearly incidence and mortality rates increased by 2.4% and 2.9%, respectively, during these time periods.
The results from the current study suggest that both over-diagnosis and a real increase in the occurrence of PTC have contributed to the observed trends in thyroid cancer incidence. The authors highlight the need for future studies to discern the specific environmental or lifestyle factors behind the increase, but also stress that thyroid cancer can be treated very successfully with surgery and radiation, if detected at an early stage. The study was published in the April 4th issue of the Journal of the American Medical Association.