Thyroid Cancer Screening in South Korea Increases Detection of Papillary Cancers with No Impact on Other Subtypes or Thyroid Cancer Mortality

BACKGROUND: The incidence of thyroid cancer has increased worldwide. The country where the incidence has increased most is South Korea. The goal of this study is to understand the magnitude of association between opportunistic thyroid cancer screening and thyroid cancer incidence, thyroid cancer subtype, and disease-specific mortality. METHODS: We used the 2010 Korea Community Health Survey, which queried 226,873 individuals if they had been screened for thyroid cancer in the last two years. Thyroid cancer incidence data from 2008 to 2010 were obtained from the Korea Cancer registry data, and mortality data from 2007-2010 were obtained from the Statistics Korea database. The ecological association between thyroid screening and thyroid cancer incidence and mortality by age and sex were examined across Korea's 16 administrative regions by general linear regression models. RESULTS: Between 2008 and 2010, the incidence of thyroid cancer was 64.1 per 100,000 individuals: the incidence in females was 107.3 and in males was 21.1. There was a strong positive correlation between regional thyroid cancer screening and regional thyroid cancer incidence (r = 0.77, [95% confidence interval 0.70-0.82]). The magnitude of correlation was higher for females (r = 0.88 [CI 0.83-0.92]) than in males (r = 0.76 [CI 0.67-0.84]) in any age group. Thyroid screening was only associated with increased detection of papillary thyroid cancer (r = 0.74 [CI 0.59-0.88]); and not associated with mortality (r = -0.08 [CI -0.59-0.63]) due to thyroid cancer. CONCLUSIONS: The magnitude of association between thyroid cancer screening in South Korea and the incidence of thyroid cancer strongly suggests that screening is the most important driver of the epidemic of thyroid cancer, particularly among females. Thyroid cancer screening, however, was only associated with the increase of one tumor histology, papillary thyroid cancer, and it did not have any association with thyroid cancer mortality. The extent to which opportunistic thyroid cancer screening is converting thousands of asymptomatic persons to cancer patients without any known benefit to them needs to be examined carefully.