The increased incidence of thyroid cancer appears to be associated with an “epidemic of diagnosis” and not disease, according to a new study. An increase in thyroid cancer previously has been reported, largely due to the detection of small papillary cancers, a common and less aggressive form of the disease, according to the study background.

The authors, Louise Davies, MD, MS, of the VA Medical Center in White River Junction, Vermont, and H. Gilbert Welch, MD, MPH, of the Dartmouth Institute for Health Policy & Clinical Practice in Hanover, New Hampshire, analyzed data for patients with thyroid cancer diagnoses between 1975 and 2009 in nine areas of the country using the Surveillance, Epidemiology, and End Results (SEER) Program: Atlanta, Connecticut, Detroit, Hawaii, Iowa, New Mexico, Utah, the San Francisco-Oakland area in California, and the Seattle-Puget Sound area of Washington.

Since 1975, the incidence of thyroid cancer has nearly tripled from 4.9 to 14.3 per 100,000 people, with virtually the entire increase due to papillary thyroid cancer (from 3.4 to 12.5 per 100,000 people). The absolute increase in thyroid cancer among women (from 6.5 to 21.4 = 14.9 per 100,000 women) was almost four times greater than for men (from 3.1 to 6.9 = 3.8 per 100,000 men). The mortality rate has remained stable since 1975 at about 0.5 deaths per 100,000 people, according to the results.

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The authors suggested that the jump in incidence is due to an increase in diagnosis and possibly overdiagnosis of papillary thyroid cancer, which can be present in patients without symptoms. Overdiagnosis occurs when a person is diagnosed with a condition that causes no symptoms and may cause them no eventual harm.

Response to overdiagnosis could ultimately include active surveillance without treatment of the asymptomatic cancers, relabeling some of them as other than cancer, and more closely investigating risk factors for cancer, the authors wrote in the study. They also suggest that physicians explain to patients that many of these small cancers will never grow and cause harm to the patient, although it is not possible to know which diagnosed cancers will fall into that category.

“We found that there is an ongoing epidemic of thyroid cancer in the United States. It does not seem to be an epidemic of disease, however. Instead, it seems to be substantially an epidemic of diagnosis: thyroid cancer incidence has nearly tripled since 1975, while its mortality has remained stable,” the authors concluded. The study was published in JAMA Otolaryngology—Head & Neck Surgery (2014; doi:10.1001/jamaoto.2014.1).