Decreasing trends in thyroid cancer incidence in South Korea: What happened in South Korea?

Abstract

Background: South Korea has the highest incidence of thyroid cancer in the world. Our study examined the trends in thyroid cancer incidence by the histologic type, cancer stage, and age group and explored possible factors that affected thyroid cancer trends.

Methods: We conducted a descriptive epidemiological study using the national cancer registry data and cause of death data from 1999 to 2016 in South Korea. Age-standardized rates were calculated using Segi's world standard population. Joinpoint regression analysis was applied to determine the changing point of thyroid cancer trends according to histologic type; Surveillance, Epidemiology, and End Results (SEER) summary stage; and age groups by sex.

Results: The age-standardized incidence of thyroid cancer in both men and women increased from 6.3 per 100,000 people in 1999 to 63.4 per 100,000 in 2012 but declined from 2012 to 2016, before the debates for over diagnosis of thyroid cancer began in 2014. The age-standardized mortality rate of thyroid cancer, incidence of distant thyroid cancer, and incidence of regional and localized thyroid cancer started to decline since early 2000, 2010, and 2012, respectively. In addition, thyroid cancer prevalence in thyroid nodules showed decreasing trends from 1999-2000 to 2013-2014.

Conclusions: The incidence of thyroid cancer began declining from 2012, before the debates for over diagnosis of thyroid cancer began in 2014. Changes in guidelines for thyroid nodule examinations may have affected this inflection point. Moreover, the debates for over diagnosis of thyroid cancer may have accelerated the decline in thyroid cancer.

Keywords: South Korea; incidence; mortality; reservoir; thyroid neoplasm.

FIGURE 1

Joinpoint regression analysis for thyroid cancer mortality rates of thyroid cancer. Footnotes: The age‐standardized rates are presented as mortality cases per 100,000 people using Segi's world standard population as standard population. Joinpoint regression analysis was used to determine whether there were significant changes in trends. The lines represent the estimated trends from the joinpoint regression, and the dots represent the observed (real) rates

FIGURE 2

(A) Joinpoint regression analysis for thyroid cancer incidence rates of thyroid cancer by SEER summary stage in men. Footnotes: The age‐standardized rates are presented as incidence cases per 100,000 people using Segi's world standard population as standard population. Joinpoint regression analysis was used to determine whether there were significant changes in trends. The lines represent the estimated trends from the joinpoint regression, and the dots represent the observed (real) rates. (B) Joinpoint regression analysis for thyroid cancer incidence rates of thyroid cancer by SEER summary stage in women. Footnotes: The age‐standardized rates are presented as incidence cases per 100,000 people using Segi's world standard population as standard population. Joinpoint regression analysis was used to determine whether there were significant changes in trends. The lines represent the estimated trends from the joinpoint regression, and the dots represent the observed (real) rates