Is an epidemic of thyroid cancer really an epidemic of diagnosis?

February 25, 2014 | by

An epidemic of thyroid cancer in the U.S. is actually an epidemic of diagnosis, conclude the authors of a new report. Their analysis pointed out that, although thyroid cancer diagnoses have nearly tripled during the past 30 years, mortality rates have remained the same. To them, this means the disease has been dramatically overdiagnosed.

Screening for thyroid cancer

Thyroid cancer is overdiagnosed, a new study bluntly claims. A City of Hope expert disagrees, pointing to mortality data as proof that screening works. Here, a woman undergoes screening for thyroid abnormalities.

City of Hope thyroid cancer expert John Yim, M.D., associate professor of surgery, strongly disagrees.

“I think ‘overdiagnosis’ is an inappropriate term,” said Yim, who was not involved in the research published recently in JAMA Otolaryngology-Head & Neck Surgery. “All of the patients are presumed to have been accurately diagnosed with thyroid cancer, primarily papillary thyroid cancer [the most-common, least-aggressive kind]. The question is whether the thyroid cancer identified, particularly when small, will progress to become symptomatic or deadly.”

That remains the nettlesome question both for physicians and for patients. Is watching and waiting – dubbed “active surveillance” – as safe for small tumors as surgical removal of them? 

The study's authors conceded that question to be a crucial one. “We will be looking hard at the question of watchful waiting for small papillary thyroid cancers, and we are going to be asking hard questions about whether we should even be looking for them,” the report's lead researcher, H. Gilbert Welch, M.D., M.P.H., professor of medicine at Dartmouth Institute for Health Policy & Clinical Practice, told HealthDay in an interview about the new study.

The notion of potentially abandoning the search for small tumors disturbs Yim. “We need to keep looking for the possibility of thyroid cancer,” Yim told KABC-TV health reporter Denise Dador in a recent interview about the report. “Thyroid cancer can still kill people.”

One of Yim’s patients, Steve Yao, did not have the customary symptoms of thyroid cancer such as hoarseness, difficulty swallowing or a nodule on his neck, but when he learned that he had an elevated cancer marker in his blood, he insisted on a biopsy. He eventually came to Yim, who removed the tumor before it metastasized. His thyroid tumor turned out to be a potentially deadly one-centimeter medullary thyroid cancer.

“I’m lucky that I found it because this type of cancer is more aggressive,” Yao told Dador.

In the study, Welch and fellow researcher Louise Davies, M.D., M.S., VA Medical Center in White River Junction, Vt., analyzed data from nine areas within the National Cancer Institute’s Surveillance, Epidemiology and End Results (SEER) program, representing about 10 percent of the U.S. population. Patients studied were from Atlanta, Connecticut, Detroit, Hawaii, Iowa, New Mexico, San Francisco-Oakland, Seattle-Puget Sound, Wash., and Utah.

Researchers explored the cases of men and women older than 18 who were diagnosed as having a thyroid cancer between 1975 and 2009.

They found that, since 1975, the incidence of thyroid cancer has nearly tripled, from 4.9 people to 14.3 people per 100,000. They wrote that “virtually the entire increase was attributable to papillary thyroid cancer” (from 3.4 people per 100,000 to 12.5 people per 100,000). The absolute increase in thyroid cancer among women (from 6.5 women to 21.4 women – 14.9 percent for 100,000 women) was almost four times greater than for men (from 3.1 men to 6.9 men – 3.8 percent per 100,000 men).

Yim faults the conclusions drawn from the SEER data.

“Clearly some of these thyroid cancers will not only become symptomatic but deadly, resulting in a consistent 0.5 deaths out of every 100,000 people every year.  This is higher than testicular, anal, bone and joint, Hodgkin lymphoma, and small intestinal cancer death rates [from seer.cancer.gov], and presumably basal cell and squamous cell cancer of the skin [not in seer.cancer.gov],” he said.

“A significantly larger number of patients with thyroid cancer will not die but will not be cured either, and others will progress to local metastasis and even distant metastasis, which may take years. None of these patients can be analyzed in the SEER data."

Yim continued: “The greatest danger in interpreting the SEER and the National Center for Vital Statistics data is that these data do not provide any insight into the mechanism of what we are seeing, yet multiple attempts at providing such insight are made anyway. For example, one assumption pointing to overdiagnosis is made simply because there is a large increase in incidence of thyroid cancer while mortality remains stable. The implication made is that most of the new cancers identified aren’t killing patients. Notwithstanding the inability to identify which new cancers identified are killing the patients and which ones aren’t, this assumption simply hasn’t been tested at all in this study.

“The reason that the mortality rate has stayed the same for 30 years despite the increase in incidence of thyroid cancer,” said Yim, “is because we are finding them early.”

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Learn more about thyroid cancer risks, symptoms and treatments.