South Korean Study Sparks Warnings About the Hazards of Overscreening

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H. Gilbert Welch, MD, MPH

I think we need more balance in the messaging, because for years, the only message that the general public has been hearing is that you should be looking for early forms of every disease, the earlier the better. We need more nuance than that.

—H. Gilbert Welch, MD, MPH

An “epidemic of diagnosis” of thyroid cancer is occurring in South Korea and “absolutely could happen here,” according to H. Gilbert Welch, MD, MPH, Professor of Medicine at the Dartmouth Institute for Health Policy and Clinical Practice, Hanover, New Hampshire. Dr. Welch is coauthor of an article in The New England Journal of Medicine1 reporting that widespread and inexpensive thyroid cancer screening in South Korea led to a 15-fold increase in the rate of thyroid cancer diagnoses there over the past 2 decades. The authors suggest that if the United States and other countries “want to prevent their own ‘epidemic,’ they will need to discourage early thyroid-cancer detection.”

In an interview with The ASCO Post, Dr. Welch said, “As a profession, this is a place where we need to actively discourage early detection, because so many people have thyroid nodules, and such a high proportion of them could be said to be cancer.” Virtually all of the tumors found in the South Korean screening program were papillary thyroid tumors, “the vast majority of which will not produce symptoms during a person’s lifetime,” according to the journal article.

Problem Is Not Just Screening

“The problem is not just screening, as in people coming in for an ultrasound,” Dr. Welch stated. Problems also arise when patients are encouraged to do neck exams. “We shouldn’t have the public starting to worry and systematically try to feel bumps in their thyroid. That would be the wrong thing to do,” Dr. Welch said.

“We’ve got another issue,” he added, “which is that we have enough imaging going on near the thyroid that physicians stumble on to thyroid nodules” while performing carotid duplex or other scans. And “once they’re stumbled on,” it sets in motion the sequence of diagnosis and treatment. “It would be very useful for us also to discourage that kind of action,” Dr. Welch noted.

“The first thing is to mitigate as much unnecessary testing as possible. We’ve got people going into scanners too frequently anyway. But when thyroid abnormalities are identified, patients shouldn’t be scared about them, and for most small thyroid nodules that are incidentally detected, we shouldn’t be pursuing them,” he said. “So it has to be broader than just saying, don’t screen for thyroid cancer using ultrasound.”

Dr. Welch applauds the recently released guidelines from the American College of Radiology recommending that incidentally detected thyroid nodules less than 1.5 cm in size (< 1 cm in patients younger than age 35) recieve no further evaluation.2

Consequences of Treatment

“The majority of patients given diagnoses of thyroid cancer have their thyroid removed,” Dr. Welch wrote in an op-ed piece for The New York Times.3 According to the data for South Korea, virtually all are treated and roughly two-thirds of the patients had radical thyroidectomy and require lifelong thyroid replacement therapy. “An analysis of insurance claims for more than 15,000 Koreans who underwent surgery showed that 11% had hypoparathyroidism and 2% had vocal-cord paralysis,” according to The New England Journal article.

Dr. Welch noted that it “is a very useful step to move from” radical thyroidectomy to lobectomy (a less extensive surgery removing only half the thyroid) because “there is a good chance you will not need thyroid replacement, and your chance of hypoparathyroidism goes to almost 0.”

In this country, too, most people diagnosed with thyroid cancer “do get thyroid-directed surgery,” Dr. Welch said. From the Surveillance, Epidemiology, and End Results (SEER) data, “it looks like most are coded as radical thyroidectomy,” he added.

Some Opt for Observation

“Some doctors are willing to manage these small cancers with observation. And, of course, that makes more sense,” Dr. Welch stated.

A news article about the thyroid cancer screening study reported in The New York Times: “A few places, like Memorial Sloan Kettering Cancer Center in Manhattan, offer patients with small tumors the option of simply waiting and having regular scans to see if the tumor grows. But few patients have joined the program.”4

“I understand that,” Dr. Welch said. “It is always hard once you say someone has cancer; in some sense, the horse is out of the barn. But it does make it clear that more and more doctors are getting sensitized to this problem—not just in thyroid cancer, but in early cancer detection in general. And that’s good.”

How Do We Know It’s Overdiagnosis?

Although the rate of diagnosis of thyroid cancer in South Korea has increased 15-fold since 1993, the mortality rate has remained stable. “If the screening were saving lives,” Dr. Welch noted, “the death rate would decline or increase more slowly as the epidemic spread—but not stay perfectly flat.”

The mass screenings for thyroid cancer in South Korea were not begun as a result of any particular perceived high risk, Dr. Welch stated. As The New England Journal article pointed out, the screenings were an add-on to a 1999 national cancer-screening program. “Although thyroid-cancer screening was not included in the program, providers frequently chose to offer screening with ultrasonography as an inexpensive add-on for $30 to $50,” according to the journal article.

“Remember, this is a single-payer system, but it has an active private sector that is delivering it—fee-for-service doctors and hospitals—and this was an easy extra service for them to sell. They already had the ultrasound machines. They were very common, and there was all this messaging about early cancer detection. They could add on a thyroid ultrasound, and patients would pay for it out of pocket,” Dr. Welch said. “It just sort of worked well with the general promotion of screening…. Then you generate a fair amount of money afterward, because you find a lot of nodules and get a lot of biopsies,” he continued.

“I think understanding this example could help people understand how far wrong you can go with an early-detection strategy,” Dr. Welch said. “You can end up treating a whole lot more people for something that was never going to bother them.”

He added, “I think we need more balance in the messaging, because for years, the only message that the general public has been hearing is that you should be looking for early forms of every disease, the earlier the better. We need more nuance than that.” ■

Disclosure: Dr. Welch reported no potential conflicts of interest.


1. Ahn HS, Kim HJ, Welch HG: Korea’s thyroid-cancer “epidemic”—screening and overdiagnosis. N Engl J Med 371:1765-1767, 2014.

2. Hoang JK, Langer, JE, Middleton WD, et al: Managing incidental thyroid nodules detected on imaging: White paper of the ACR Incidental Thyroid Findings Committee. J Am Coll Radiol 2014 (in press).

3. Welch HG: An epidemic of thyroid cancer? New York Times, November 5, 2014.

4. Kolata G: Study points to overdiagnosis of thyroid cancer, New York Times, November 5, 2014.

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