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Thyroid

Did thyroid cancer screening in South Korea save lives?

It multiplied diagnoses. The published evidence is that the great majority of those diagnoses were of cancers that would never have caused harm.

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Answer

Screening multiplied thyroid cancer diagnoses in South Korea without a matching change in deaths: incidence rose 6.4-fold between 1999 and 2008, with 94.4 percent of the increase consisting of tumours smaller than 20 mm found mainly by screening, while an international analysis attributed more than 85 percent of Korean female cases in 2013–17 to overdiagnosis.

Key takeaways

  • Thyroid cancer incidence in South Korea rose 6.4-fold between 1999 and 2008, from 6.4 to 40.7 per 100,000.
  • 94.4 percent of that increase consisted of tumours smaller than 20 mm, detected mainly by screening, and 97.1 percent of the total increase was localised or regional disease.
  • The authors of that nationwide study concluded the epidemic was due to increased detection of small tumours, most likely overdetection.
  • A study of 63 countries estimated that more than 85 percent of thyroid cancer cases in Korean women during 2013–17 were overdiagnosed, and 75.6 percent of cases across all registries examined.
  • Korea's standardised thyroid cancer mortality rate rose until the early 2000s and has declined steadily since, through both the rise and the fall in diagnoses.

Overdiagnosis means finding a cancer that is real under a microscope but would never have caused symptoms or death in the person's lifetime. It is not a misdiagnosis. The tissue is cancer; the problem is that the person was never going to be harmed by it, and treatment can only cost them.

South Korea is the most studied example of it anywhere.

What the Korean data show

A nationwide study published in The BMJ in 2016 reviewed medical records for representative samples of Korean thyroid cancer patients diagnosed in 1999, 2005 and 2008, and asked how the tumours had been found.

94.4%

of the increase in Korean thyroid cancer incidence between 1999 and 2008 consisted of tumours smaller than 20 mm, detected mainly by screeningPark S et al., The BMJ, 2016

Incidence over that period rose 6.4-fold, from 6.4 to 40.7 per 100,000. Of the total increase, 97.1 percent was localised or regional disease. The authors concluded that the epidemic was due to increased detection of small tumours, most likely overdetection.

Deaths did not follow diagnoses

Korea's standardised thyroid cancer mortality rate rose until the early 2000s and has declined steadily since. Diagnoses meanwhile peaked in 2012, fell sharply to 2015, and have risen again since. The death rate shows no corresponding inflection in either direction.

How Korea compares

An analysis of 63 countries published in The Lancet Diabetes & Endocrinology in 2024 estimated that more than 85 percent of thyroid cancer cases in women were overdiagnosed in South Korea, Cyprus, China and Türkiye. Across all the registries it examined, 1,736,133 of 2,297,057 cases — 75.6 percent — were attributable to overdiagnosis.

Korea is no longer unusual in having this problem. What distinguishes it is the length of its record: it has more years of data after the peak than anywhere else.

What this means for someone offered a scan

The finding is about screening people with no symptoms, and it is not an argument against investigating a lump, a change in the voice, or any other reason a clinician has to examine the thyroid. Nor does it say that a thyroid cancer already found should be ignored: what happens to a confirmed small cancer is a separate question, and Korea now has a guideline on watching rather than removing it.

Sources

  1. 1

    Park S, Oh CM, Cho H, Lee JY, Jung KW, Jun JK, et al.

    Association between screening and the thyroid cancer "epidemic" in South Korea: evidence from a nationwide study

    BMJ 2016;355:i5745

    doi:10.1136/bmj.i5745 · PMID:27903497

    https://doi.org/10.1136/bmj.i5745
  2. 2

    Li M, Dal Maso L, Pizzato M, Vaccarella S

    Evolving epidemiological patterns of thyroid cancer and estimates of overdiagnosis in 2013-17 in 63 countries worldwide: a population-based study

    The Lancet Diabetes & Endocrinology 2024;12(11):824-836

    doi:10.1016/s2213-8587(24)00223-7 · PMID:39389067

    https://doi.org/10.1016/s2213-8587(24)00223-7
  3. 3

    Yoon YJ, Seo JM, Kim JS, Choi YM, Kim WG

    Long-Term Trends in Thyroid Cancer Incidence and Mortality in Korea: Analysis of Korean National Data

    Endocrinology and Metabolism 2026

    doi:10.3803/enm.2025.2807 · PMID:42324644

    https://doi.org/10.3803/enm.2025.2807