The rapid increase in thyroid cancer incidence that has occurred since the 1990s — considered an "epidemic of overdiagnosis," has extended beyond high-income countries to less affluent settings, where unnecessary — and sometimes opportunistic — screening could continue to thrive.
"The impact of overdiagnosis on the increasing incidence of thyroid cancer highlighted in our report is a warning sign for countries with growing economies, where diagnostic technologies are increasingly and routinely offered, usually in exchange for payment, despite evidence that the harms far outweigh benefits," the authors say.
"Overdiagnosis could turn healthy people into patients, and expose them to unnecessary harms and lifelong treatments," say Mengmeng Li, PhD, of the International Agency for Research on Cancer, Lyon, France, and colleagues in their article published in June issue of Lancet Diabetes & Endocrinology.
With their previous research showing high rates of overdiagnosis in high-income countries, for this new analysis, they sought to evaluate whether similar patterns were occurring in less affluent settings.
They examined data from population-based cancer registries in 26 countries on four continents, looking at all cases of thyroid cancer reported between 1998 and 2012 in men and women aged 15 to 84.
A Global Public Health Problem
The results showed that while the incidence of thyroid cancer steadily increased from 1998 to 2002 and from 2008 to 2012 in all high-income countries, similar trends were also seen in less affluent nations, particularly in China, Colombia, Lithuania, and Belarus.
The increases were consistently greater among middle-aged women aged 35-64 years in all countries.
To determine what proportion of the higher incidence was overdiagnosis, the authors turned to historic age-specific thyroid cancer incidence data prior to the introduction of ultrasound and then looked at the progressive departure from that pattern, likely the result of the increased detection by ultrasound of thyroid nodules in middle-aged adults.
The results showed the proportion of thyroid cancer cases in women estimated to be attributable to overdiagnosis between 2008 and 2012 was as much as 93% in South Korea, 91% in Belarus, 87% in China, 84% in Italy and Croatia, and 83% in Slovakia and France.
Proportions attributable to overdiagnosis were lower in Denmark (66%), Norway (65%), Ireland (63%), UK (58%), Japan (55%), and Thailand (44%).
Women were much more likely to be overdiagnosed than men, with an approximate ratio of 3:1 in all countries; however, mortality and prevalence of thyroid cancer in autopsies were similar between genders.
Although researchers only looked at data up until 2012, Li said even in that year "the amplitude of the phenomenon" was "already large and is increasing rapidly over time."
Figures for periods subsequent to those assessed in the study "are likely to be higher."
And the overdiagnosis is particularly remarkable in the context of the true risk of thyroid cancer, senior author Salvatore Vaccarella, PhD, told Medscape Medical News.
"What is surprising is the magnitude of this. Without overdiagnosis, thyroid cancer would probably still be a relatively rare cancer," he said.
"Currently, it is the fifth most commonly diagnosed cancer in women of all ages and is third in women under 50 years of age. And the rates are still rising fast."
"Overdiagnosis of thyroid cancer is still rapidly expanding in many high-income countries, and for the first time, we document and quantify the phenomenon also for several middle-income socioeconomically transitioning countries," he observed.
"In short, it is a global public health problem."
Guidelines, Physicians: No Symptoms Should Mean No Screening
With the implications of overdiagnosis ranging from physical, psychological in terms of the patient, and significant personal as well as societal costs, most international guidelines explicitly recommend against screening asymptomatic individuals and call for active surveillance of microcarcinomas that are detected.
The messaging appears to be making a difference.
As reported in research by American authors discussing the thyroid cancer epidemic from a 2017 perspective, the overdiagnosis situation in South Korea prompted a group of physicians there to make a high-profile public appeal in print and on television recommending against thyroid screening with ultrasound.
The result was a 35% reduction in the number of thyroidectomies performed in the subsequent year.
"This seems to be a striking example that the issue of overdiagnosis and overtreatment resonates with patients, and that public awareness can lead to changes in behavior," say the US authors of that article.
Senior author Louise Davies, MD, of the VA Outcomes Group, in White River Junction, Vermont, told Medscape Medical News the new study sheds more light on this issue.
"Even though the data only go through 2012, I think they give a nice snapshot of what's happening across the globe with thyroid cancer incidence in countries of different levels of development," she said.
The findings underscore that "it's important that people are educated about the limits of medical testing and that sometimes when we see abnormalities we are truly catching a cancer early, but sometimes we're seeing things that have been there a long time and may not change or become a problem in the future," Davies remarked.
Important to Know What Size of Cancers Are Being Detected
One particular concern about overdiagnosis in middle-income countries is that the common approach of active monitoring may be more difficult in these settings, Davies added.
"In order to manage overdiagnosis, the healthcare systems in those countries have to think about whether they have the infrastructure for active monitoring and whether the patients will show up for the monitoring — so that's a challenge."
Also, she noted that the new study does not detail the size of cancers detected.
"We don't know much about the size of the cancers being detected and whether these are truly the small asymptomatic cancers that we are worried about being overdiagnosed."
"Probably, at least some of what we're seeing is appropriate detection of cancers that, before there was economic development, were in fact being missed and people were dying of," she said.
"So while overdiagnosis can be occurring, some of this represents better detection of disease overall, and that's a good thing actually."
The authors and Davies have reported no relevant financial relationships.
Lancet Diabetes Endocrinol. 2020;8:P468-470. Full text
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Cite this: Thyroid Cancer Overdiagnosis Reaches Beyond Affluent Regions - Medscape - Jun 09, 2020.