Thyroid Cancer Still Overdiagnosed in the U.S., Study Finds

Despite efforts to curb overdiagnosis of thyroid cancer, the issue has continued to plague U.S. healthcare, according to results from a retrospective, population-based study.

Researchers found that while the incidence of thyroid cancer plateaued over the period from 2009 to 2019, it did so at peak levels after a period of substantial increase between 1975 and 2009, “suggesting that overdiagnosis remains a crucial unresolved health issue,” reported Zachary Zumsteg, MD, of Cedars-Sinai Medical Center in Los Angeles, and colleagues, in Lancet Diabetes and Endocrinology.

“Even though the incidence of thyroid cancer has stabilised in the USA since the late 2010s, it is still high, with most cases attributable to overdiagnosis, as is the case in many other places worldwide,” wrote Luigino Dal Maso, PhD, of the Centro di Riferimento Oncologico di Aviano IRCCS in Aviano, Italy, and colleagues, in a commentary accompanying the study. “The opportunistic search for small lesions of the thyroid has no proven benefits in terms of reducing mortality from the disease, but instead leads to the overdiagnosis and overtreatment of many, often young, asymptomatic individuals.”

Using data on more than 91,000 thyroid cancer patients from the National Cancer Institute’s Surveillance, Epidemiology, and End Results database and the National Center for Health Statistics database, Zumsteg and colleagues found that the annual incidence of thyroid cancer increased gradually from 5.0 cases per 100,000 people in 1975 to 14.6 cases per 100,000 people in 2009. Thyroid cancer incidence then plateaued until 2019 at a rate of 14.1 cases per 100,000 people.

At the same time, the absolute rate of metastasis at diagnosis remained stable at 0.4 cases per 100,000 people in both 1975 and 2019. The same held true with mortality rates specific to thyroid cancer as they remained unchanged at 0.5 deaths per 100,000 people in 1975 and in 2019.

Moreover, they found that this plateau occurred in almost all age groups, starting from age 25 years, suggesting a time period effect “as a result of shifts in clinical practice.”

“People visiting the doctor in 1975 were less likely to receive imaging than those visiting the doctor in 2019,” Zumsteg said in a press release. “So today doctors are finding thyroid nodules that would not have been detected in previous decades, leading to more biopsies and diagnoses of small, slow-growing thyroid cancers that might not require treatment.”

Zumsteg and colleagues also determined that while an increase in incidence was reported across all age groups, the increase was largest among women between the ages of 40 and 69 and among men 50 to 79 years of age.

“These period-dependent age effects might be explained by the ages at which women and men most frequently interact with the health-care system, leading to an increased likelihood of receiving imaging that detects an incidental thyroid nodule,” Zumsteg and colleagues wrote. They also observed that since women are more frequent users of healthcare in the U.S., increased healthcare interactions could explain the higher incidence of thyroid cancer in women.

“Collectively, these data strongly suggest that both the age-specific and sex-specific variations seen in the incidence of thyroid cancer in current clinical practice are primarily driven by period-dependent increases in the overdiagnosis of clinically indolent thyroid cancers,” they wrote.

As for why the incidence rates have plateaued since 2009, Zumsteg and colleagues said shifts in primary practice patterns are primarily responsible.

For example, they pointed out that over the past decade the Endocrine Society published Choosing Wisely guidelines that recommended against routine thyroid ultrasonography in patients with atypical thyroid function test results without any palpable abnormality. In addition, in 2017, the U.S. Preventive Services Task Force recommended against routine screening for thyroid cancer in asymptomatic adults.

“However, official guidelines recommending against screening for thyroid cancer have thus far only been able to halt the increase in thyroid cancer diagnoses rather than resulting in a return to significantly reduced rates of incidence and overdiagnosis,” wrote Dal Maso and colleagues in their commentary. “Overall, Chen and colleagues’ findings suggest that there is still a large pool of individuals with prevalent thyroid nodules who, if screened, could continue to be overdiagnosed with thyroid cancer unless stronger calls against the excessive scrutiny of the thyroid and aggressive management of small nodules are put in place.”

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