Largely owing to the diagnostic prowess of ever-improving imaging technologies—mainly CT, ultrasound and MRI—more than 470,000 women and 90,000 men were overdiagnosed with thyroid cancer between 1987 and 2007 across 12 bellwether countries.

Worse yet, most of these patients were subsequently overtreated.

So found researchers at the World Health Organization’s International Agency for Research on Cancer (IARC) in Lyon, France, whose diagnosis of a worldwide overdiagnosis “epidemic” posted online Aug. 18 as commentary the New England Journal of Medicine.

Lead author Salvatore Vaccarella, PhD, and colleagues also point to stronger medical surveillance and easier access to healthcare services as factors driving the “massive increases” in the detection of small, nonlethal lesions in the thyroid gland.

The researchers issued their call to caution after reviewing cancer-registry data in the IARC’s Cancer Incidence in Five Continents.

Using as a reference populations in countries with long-standing cancer registries, they diagrammed age-specific trends in thyroid-cancer incidence in the 1960s, before ultrasonography was introduced in the late 1970s.

Then they developed a historical age curve to estimate the number of cases that would have been expected if thyroid cancer had continued to be detected primarily through manual palpation.

“The shape of the age-specific curves has changed dramatically since the 1980s, albeit to different extents in various countries,” write the authors, who zeroed in on these trends in Australia, Denmark, England, Finland, France, Italy, Japan, Norway, the Republic of Korea, Scotland, Sweden and the U.S.

Incidence has progressively increased among middle-aged women and, to a lesser but still significant extent, men.

“We attribute the excess cases beyond the number predicted by the multistage model to diagnoses of asymptomatic disease subsequent to improved diagnostic technology and increased surveillance, predominantly in young or middle-aged populations,” the authors write.

Among their key insights:

• Major changes in observed age curves for women emerged in the “countries most affected by the thyroid-cancer ‘epidemic,’” including the U.S., Italy and France.
• Increases in incidence in the U.S., Australia and Italy began in the 1980s—right around the time ultrasound machines became standard equipment in gynecologic and obstetric clinics—and were particularly prominent among women younger than 45. The wide technology adoption for this demographic, the authors note, clearly “favored opportunistic examinations of the thyroid gland in women of reproductive age.”
• The team observed a striking increase among South Korean women 50 to 59 years of age, from about 35 cases per 100,000 women in 1998–2002 to more than 120 cases per 100,000 women in 2003–2007.
• Sudden changes in thyroid-cancer incidence accompanied large-scale thyroid-gland surveillance in “purportedly high-risk populations.” In Japan’s Fukushima Prefecture, for example, thyroid-cancer incidence among screened children and adolescents “was approximately 30 times as high as the national average just a few months after intensive screening programs for these age groups began in response to the 2011 nuclear accident.”

The authors stress that overdiagnosis ought not be dismissed as a necessary and acceptable cost for health systems wishing to take a better-safe-than-sorry stance.

“It’s important to bear in mind that the vast majority of patients who received a diagnosis of thyroid cancer in the countries we studied underwent total thyroidectomy,” they write, “and a high proportion also received other harmful treatments (neck lymph-node dissection and radiotherapy)—practices recently discouraged in the guidelines of the American Thyroid Association.”

What’s more, studies from Japan have shown that immediate surgery and watchful waiting are equally effective in averting deaths from thyroid cancer, the authors note, adding that only a small minority (3.5 percent) of 1,235 Japanese patients with papillary microcarcinomas who were followed for an average of 75 months had clinical disease progression—and none died.

The examples of South Korea, the United States, Italy and France “suggest that other countries should exercise caution against systematic screening for thyroid cancer and overtreatment of small nodules (<1 cm),” Vaccarella et al. write. These examples suggest that “watchful-waiting approaches should be considered a research priority and a preferable option for patients with low-risk papillary thyroid cancers.”