South Korea's thyroid cancer rise: a cautionary tale?

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South Korea's thyroid cancer rise: a cautionary tale?
Medscape, Nick Mulcahy

N Engl J Med. 2014;371:1765-1767. Abstract

South Korea's fast-rising rate of thyroid cancer in the past two decades appears to be the result of commonplace screening and is a "cautionary tale for the rest of the world," say the authors of a Perspective published in the November 6 issue of the New England Journal of Medicine. The caution to be found in the Korean tale is that, "despite the dramatic increase in incidence, mortality [in South Korea] from thyroid cancer remains stable," write Hyeong Sik Ahn, MD, PhD, and Hyun Jung Kim, PhD, from the Department of Preventive Medicine, Korea University in Seoul and H. Gilbert Welch, MD, from Dartmouth Institute for Health Policy and Clinical Practice in Hanover, New Hampshire.

This combination of factors indicates "overdiagnosis," say the trio. The authors report that, from 1993 to 2011, the incidence of thyroid cancer increased about 15-fold, from less than 5 per 100,000 population to almost 70 per 100,000. Over the same period, thyroid cancer mortality was nearly a flat line — just above 0 per 100,000 — and rose very little, according to a graph in the new paper, for which the authors used data from Korean national databases.

Thus, there is not a true "epidemic" of clinically significant thyroid cancer, the authors suggest, but instead an overuse of screening.

Small papillary thyroid cancers are present in at least one third of adults at autopsy, write the authors, citing other research. But the "vast majority" will not produce symptoms, they say. "As the South Korean data show, all it takes to expose this reservoir is ultrasonographic screening," write the authors. Other countries "will need to discourage early thyroid-cancer detection" if they "want to prevent their own 'epidemic'," they conclude. Those countries in particular are ones that have seen their own recent increase in thyroid cancer, such as France, China, Australia, Canada, and the United States, they also emphasize.

The new paper is valuable but, as an essay with some new data presented briefly, it is not a "definitive" study, said Raymon Grogan, MD, from the endocrine surgery group at the University of Chicago in Illinois in an interview with Medscape Medical News. He was not involved with the essay. The paper also has some "irritating" omissions and vagaries, he said. For example, the authors overemphasize the uniqueness of the South Korean incidence rate, he said. "Their incidence and mortality graph looks pretty much the same as ones from other countries."

"It is true that Korea's rate of thyroid cancer has grown somewhat more rapidly than other countries, but there are increasing rates worldwide that are alarming," he added.

The paper also suggests that thyroid screening with ultrasonography is widespread in South Korea — but that is not the case, said Dr Grogan, who coincidently has South Korean in-laws. About 10% to 15% of Koreans get their thyroid screened with ultrasonography, he said, citing other research. However, in the new paper, the authors imply that screening is much more common but do not provide any specific numbers, said Dr Grogan. Instead, the authors write that "many general practitioners [in South Korea} have ultrasonography machines in their offices and commonly scan the thyroid." Dr Grogan also believes that "the term 'overdiagnosis' is being used incorrectly by this group."

Thyroid cancer has such a high 5-year overall survival rate (about 97%) that it cannot be expected that mortality will significantly increase as incidence climbs, he explained. "A concomitant mortality increase would be expected for, say, pancreatic cancer, but not thyroid cancer," he said. Thus, if a hallmark of overdiagnosis cannot be expected to be seen, then the term is not fitting, he suggested. Dr Grogan believes that the paper's public health perspective is a limitation for clinicians. "The big question is: Do these patients need surgery?" he said. "The answer can't be that you do nothing." At the same time, Dr Grogan advocates for clinical trials that explore other management options for patients with thyroid cancer.

Thyroid cancer is a candidate for active surveillance, but protocols are needed and must be investigated. Currently, researchers in Japan are "leading the way" with related prospective studies, he said. In the United States, thyroid cancer research is "significantly underfunded," wrote Dr Grogan and colleagues in an earlier paper (Cancer Epidemiol Biomarkers Prev. 2013;22:1252-1259). "By 2019, papillary thyroid cancer will double in incidence and become the third most common cancer in women of all ages," they wrote. Meanwhile, in 2009, thyroid cancer received only $14.7 million (ranked 30th) in research funding from the National Cancer Institute.

The authors and Dr Grogan have disclosed no relevant financial relationships.