BACKGROUND
The number of people diagnosed with thyroid cancer every year in the United States started rising in 1974, with more cases found each year thereafter until 2014. However, the number of people in the United States dying each year from thyroid cancer did not change during this time period, suggesting that at least some of the new cases of thyroid cancer found each year were not actually dangerous. In addition, many experts believe that the reason for increasing number of thyroid cancers over this time period was mostly related to improvements in thyroid cancer detection rather than an actual increase in the number of new thyroid cancers every year. Starting in 2014, the number of U.S. thyroid cancer cases per year stabilized and then, for each of the next three years (through 2017), this number actually went down.

Understanding these trends is important because this helps doctors better understand how big a problem thyroid cancer is to the United States population, why thyroid cancer might develop, and which people might have the highest risk of developing this disease. Monitoring changes in how many people die of thyroid cancer each year also helps doctors understand how effective treatments are for this disease. The research described here aims to update our knowledge of the number of thyroid cancer cases diagnosed and the number of people who die of this disease in the United States each year.

THE FULL ARTICLE TITLE
Megwalu UC, Moon PK 2022 Thyroid cancer incidence and mortality trends in the United States: 2000–2018. Thyroid. Epub 2022 Mar 15. PMID: 35132899.

SUMMARY OF THE STUDY
The authors of this study used two large databases that collect and store medical information for people living in the United States to update our knowledge of thyroid cancer incidence and mortality. Together, these two databases include medical information for 28% of the United States population. A total of 197,070 thyroid cancer cases were identified for the study timeframe using these databases. The investigators specifically collected data starting with the year 2000 and then for every subsequent year through 2018. The study confirmed previous findings that the number of thyroid cancers diagnosed increased until 2014, after which the number decreased through 2018. Death from thyroid cancer, on the other hand, increased somewhat for the most common type of thyroid cancer (papillary thyroid cancer) and for the rarest form of thyroid cancer (anaplastic thyroid cancer), but not for the less common follicular and medullary thyroid cancer subtypes.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
The study authors’ findings confirm that the number thyroid cancers in the United States went up until 2014, and then began decreasing. Similarly, the authors conclude that the reason the number of thyroid cancers started going down after 2014 was because doctors stopped trying to identify small thyroid cancers that are not dangerous, leaving these thyroid cancers undiagnosed. In contrast, the authors conclude that the increase in death from papillary thyroid cancer seen in their study is the result of a true increase in advanced (more dangerous and difficult to treat) disease. The reasons for this increase in advanced thyroid cancer is not clear but certainly is an area for additional future studies.

— Jason D. Prescott, MD PhD

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