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

Abstract

Objective To investigate whether screening for thyroid cancer led to the current “epidemic” in South Korea.Design Review of the medical records of nationally representative samples of patients with a diagnosis of thyroid cancer in 1999, 2005, and 2008.Setting Sample cases were randomly selected from South Korea’s nationwide cancer registry, using a systematic sampling method after stratification by region.Participants 5796 patients with thyroid cancer were included (891 in 1999, 2355 in 2005, and 2550 in 2008).Main outcome measures The primary outcome was age standardised incidence of thyroid cancer and the changes in incidence between 1999 and 2008 according to the methods used to detect tumours (screen detection versus clinical detection versus unspecified).Results Between 1999 and 2008, the incidence of thyroid cancer increased 6.4-fold (95% confidence interval 4.9-fold to 8.4-fold), from 6.4 (95% confidence interval 6.2 to 6.6) per 100 000 population to 40.7 (40.2 to 41.2) per 100 000 population. Of the increase, 94.4% (34.4 per 100 000 population) were for tumours less than 20 mm, which were detected mainly by screening. 97.1% of the total increase was localised and regional tumours according to the Surveillance, Epidemiology, and End Results (SEER) summary stage. Where cases were clinically detected, 99.9% of the increased incidences (6.4 per 100 000 population) over the same period were tumours less than 20 mm.Conclusion The current “epidemic” of thyroid cancer in South Korea is due to an increase in the detection of small tumours, most likely as a result of overdetection. Concerted efforts are needed at a national level to reduce unnecessary thyroid ultrasound examinations in the asymptomatic general population.

Long-term oncologic outcomes of papillary thyroid microcarcinoma according to the presence of clinically apparent lymph node metastasis: a large retrospective analysis of 5,348 patients

“…It would also offer reassurance to patients without higher-risk disease when determining AS candidates. Both improved imaging technology and molecular biomarkers show promise in this regard 7,20,21. Nevertheless, thus far, no definite biological or clinical parameters are available that can distinguish low-risk from potentially aggressive thyroid cancer, and the long-term oncological effect of delayed initial intervention has not been evaluated.…”

Overdiagnosis of thyroid cancer

“…In a linked article in The BMJ, 5 Park and colleagues extend our understanding of the issue in South Korea, which has seen a 15-fold increase in incidence over the past 10 years, 6 the highest rate of increase in the world. Using data from the National Epidemiologic Survey of Thyroid Cancer (NEST), a detailed representative sample of cancer cases from the Korea Central Cancer Registry, the researchers showed that between 1999 and 2008 the proportion of papillary thyroid cancers detected by screening in South Korea more than tripled, from 15% in 1999 to 56% in 2008.…”

Overdiagnosis: what it is and what it isn’t

“…Consider the example of thyroid cancer in South Korea. From 1999 to 2008, the incidence of thyroid cancer increased 6.4-fold,7 but 95% of these cancers were small (<20 mm), and they were detected mainly through screening 7. The mortality from thyroid cancer remained essentially unchanged over the same period 7.…”

“…From 1999 to 2008, the incidence of thyroid cancer increased 6.4-fold,7 but 95% of these cancers were small (<20 mm), and they were detected mainly through screening 7. The mortality from thyroid cancer remained essentially unchanged over the same period 7. Use of advanced imaging also leads to overdetection by finding incidentalomas—‘surprise’ abnormalities unrelated to the original reason for doing the test, for example, when a chest CT done to follow-up on a pulmonary nodule detects a small adrenal adenomas.…”