The threefold increase in thyroid cancer diagnoses in several high-income countries over the past three decades is mostly due to "overdiagnosis," the labeling of tumors that are unlikely to cause symptoms or death as thyroid cancer, according to a report published Thursday in the New England Journal of Medicine.
For the report, International Agency for Research on Cancer researchers analyzed cancer registry data from 12 high-income countries between 1987 and 2007. They found that diagnoses of thyroid cancer sharply increased after ultrasounds started to be used as a diagnostic tool. The technology enabled clinicians to find smaller, low-risk tumor growths in patients.
The report authors estimated that between 70 to 80 percent of thyroid cancer patients in the United States were overdiagnosed. In some countries, the rate was higher: In South Korea, the overdiagnosis rate was 90 percent.
The researchers argued that diagnosing small, low-risk tumor growths as thyroid cancer can do more harm than good. Report co-author Silvia Franceschi said, "The majority of the overdiagnosed thyroid cancer cases undergo total thyroidectomy and frequently other harmful treatments, like neck lymph node dissection and radiotherapy, without proven benefits in terms of improved survival."
The report authors said that patients with low-risk, small cancers with low-grade features on a biopsy would benefit more from "watchful waiting."
They pointed to research that found watchful waiting can be as effective in preventing death as surgery. In one study from Japan, only 3.5 percent of 1,235 patients with low-risk thyroid tumors saw clinical progression of the tumors over 75 months—and no patients died from the disease in that time period.
"Watchful-waiting approaches should be considered a research priority and a preferable option for patients with low-risk papillary thyroid cancers," the report authors wrote.
Luc Morris of the Memorial Sloan-Kettering Cancer Center's Department of Surgery told Medscape that the findings "are striking." He said, " It is fair to say that the large number of thyroid cancers being diagnosed represent an epidemic of diagnosis, or an epidemic of medical testing, rather than an epidemic of true disease."
Morris added, "Fortunately the thyroid cancer field has begun to accept that overdiagnosis is a very real phenomenon in thyroid cancer."
Hassan Arshad, an assistant professor at the Roswell Park Cancer Institute, told Medscape that "more research needs to be done" to assess whether patients would benefit more from the watchful waiting approach or from surgery.
Arshad said an international panel's recommendation earlier this year that a certain kind of thyroid tumor—known as encapsulated follicular variant of papillary thyroid carcinoma—be reclassified as noncancerous is evidence of an increasing recognition that thyroid cancer has been overdiagnosed (Jenkins, Medscape, 8/18; Deo et al., NBC, 8/17; International Agency for Research on Cancer release, 8/18; Hood, AFP/Yahoo News, 8/18).
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