South Korea has the highest incidence rate of thyroid cancer in the
world. Between 1999 to 2009, rates of thyroid cancer increased by more
than sevenfold, from 6.3 per 100,000 to 47.5 per 100,000 people. The
economic burden of thyroid cancer in South Korea also increased around
sevenfold, from $257m in 2000 to $1724m in 2010.
The current "epidemic" of thyroid cancer in South Korea is due to an
increase in the detection of small tumors, most likely as a result of
overdetection by screening, revealed a study published by The BMJ
‘Increase in the incidence of thyroid cancer in South Korea mainly resulted from overdetection, most likely as a result of widespread use of sensitive imaging tools.’
The researchers say concerted efforts are needed at a national level
to reduce unnecessary thyroid ultrasound examinations in the general
Overdiagnosis refers to the detection of harmless cancers that will
not cause symptoms or death during a patient's lifetime. But because it
is not possible to distinguish between lethal and harmless cancers, all
cancers detected mainly by screening are treated.
This exposes people to the potential side effects of treatment, but
without an equal expectation of benefit, because the cancer is unlikely
However, some sceptics remain unconvinced. So to investigate whether
screening for thyroid cancer led to the current "epidemic" in South
Korea, a team led by Jin Soo Lee at the National Cancer Center Research
Institute in Goyang, analyzed the medical records of 5,796 thyroid
cancer patients diagnosed in 1999, 2005, and 2008.
Most participants were women with an average age of 47 years.
Age-standardized incidence of thyroid cancer was estimated, and the
changes in incidence between 1999 and 2008 were examined according to
how the tumor was detected (by screening, by clinical symptoms
associated with thyroid disease, or unspecified).
Between 1999 and 2008, they found more than a sixfold increase in
thyroid cancer incidence, from 6.4 to 40.7 per 100,000 people.
Of the increase, 94% (34 per 100,000 people) were for tumors less
than 20 mm, which were detected mainly by screening and 97% of the total
increase was for localized and regional stage tumors.
Even where cases were clinically detected, 99.9% of the increase
(6.4 per 100,000 people) over the same period were for tumors less than
"Our study shows that the increase in the incidence of thyroid
cancer in South Korea mainly resulted from overdetection, most likely as
a result of widespread use of sensitive imaging tools (eg. ultrasound
examination)," say the authors.
"Considering the increase in thyroid cancer incidence, the financial
burden of using ultrasound to detect small tumors (and the often
unnecessary subsequent surgery) is expected to rise rapidly," they warn.
They call for concerted efforts at national level "to reduce
unnecessary ultrasound examination of the thyroid in the asymptomatic
general population, unless clinically indicated."
In a linked editorial, US researchers say these findings "strongly
suggest that the increase is due to overdiagnosis rather than an as yet
unidentified new risk factor.
Even more importantly, their data suggest that we might need to
re-examine what we include in our definition of subclinical or indolent
disease," they add.