Clinical Edge

Summaries of Must-Read Clinical Literature, Guidelines, and FDA Actions

Screening for Thyroid Cancer & Overdetection

BMJ; ePub 2016 Nov 30; Park, et al

An increase in the detection of small tumors, most likely a result of overdetection and unnecessary ultrasound examinations, may be responsible for a nationwide epidemic of thyroid cancer. A review of medical records of nationally representative samples of patients with a diagnosis of thyroid cancer in 1999, 2005, and 2008 was conducted and sample cases were randomly selected. 5,796 patients with thyroid cancer were included (n=891 in 1999; n=2,355 in 2005; n=2,550 in 2008). Researchers found:

  • Between 1999 and 2008, the incidence of thyroid cancer increased 6.4-fold from 6.4 per 100,000 population to 40.7 per 100,000.
  • 94.4% were for tumors <20 mm, which were detected mainly by screening.
  • 97.1% of the total increase was localized and regional tumors.
  • 99.9% of the increased incidences of clinically detected cases over the same period were tumors <20 mm.


Park S, Oh CM, Cho H, et al. Association between screening and the thyroid cancer “epidemic” in South Korea. [Published online ahead of print November 30, 2016]. BMJ. doi:10.1136/bmj.i5745.


In case anyone has questioned the importance of carefully thought out, evidence-based approaches to screening, the increased incidence of thyroid cancer in South Korea is an example of how screening can lead to expensive and potentially harmful over-diagnosis. The 6-fold increase in thyroid cancer in South Korea correlates with the increased use in that country of ultrasound as a screening method to detect thyroid cancers over the same period of time.1 The current study suggests that the cancers found were primarily very small cancers with no likely clinical significance, except that when they are evaluated and treated, they expose patients to the expense and side-effects of unnecessary treatment with no improvement in outcomes. Screening is always a careful balance of benefit vs harm, and the history of thyroid cancer screening with ultrasound is a lesson in the importance of ordering screening tests only when there is good evidence showing benefit. —Neil Skolnik, MD

  1. Ahn HS, Kim HJ, Welch HG. Korea’s thyroid-cancer “epidemic”— screening and overdiagnosis. N Engl J Med. 2014;371:1765-7. doi:10.1056/NEJMp1409841.