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Increasing Thyroid Cancer Incidence and Mortality in the United States

, by DCEG Staff

Anatomy of the thyroid, Terese Winslow (Illustrator)

A new analysis of thyroid cancer trends found significant increases in both incidence and mortality overall and for advanced-stage papillary thyroid cancer (PTC). The study, conducted by researchers from the National Cancer Institute, Division of Cancer Epidemiology and Genetics (DCEG), and Duke University Medical Center, was published online March 31, 2017, in the Journal of the American Medical Association.

Thyroid cancer incidence in the United States has increased more than threefold over the past four decades, mainly driven by increases in PTC, the most common type. “Historically, it has been unclear whether this trend represents a true rise in thyroid cancer cases, or if some or all of the increase could be explained by overdiagnosis of small, low-risk thyroid tumors discovered incidentally due to the introduction and increased use of sensitive imaging procedures and diagnostic techniques,” said lead author and DCEG investigator Cari Kitahara, Ph.D.

This study is the first in-depth analysis of thyroid cancer mortality and incidence rates, and looks specifically at aggressive tumors like advanced-stage PTC. Using data from SEER-9 registries and the National Center for Health Statistics, investigators examined 77,276 cases of thyroid cancer diagnosed in the United States between 1974 and 2013, of whom 2,371 died of thyroid cancer between 1994 and 2013. By combining incidence and mortality data, the researchers created a unique opportunity to evaluate incidence-based thyroid cancer mortality rates according to histology, stage, and tumor size at diagnosis. These methods help to assess what part of the increase may be a real increase, as opposed to an artifact of overdiagnosis. 

The team found that overall incidence of thyroid cancer increased by an average of 3.6 percent per year, and incidence-based thyroid cancer mortality rates increased by an average of 1.1 percent per year. For advanced-stage PTC, average yearly incidence and mortality rates increased by 2.4 percent and 2.9 percent, respectively.

These results suggest that both overdiagnosis and a real increase in the occurrence of PTC have contributed to the observed trends in thyroid cancer incidence; thyroid cancer is now the 8th most common cancer diagnosis in the United States. 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.

Reference: Lim et al. Trends in thyroid cancer incidence and mortality in the United States, 1974-2013. JAMA. March 31, 2017. doi:10.1001/jama.2017.2719