The incidence of thyroid cancer has nearly tripled since 1975, but with mortality remaining stable, researchers are considering this to be an “epidemic of diagnosis,” not an epidemic of disease, according to a recent study.
In 2006, researchers Louise Davies, MD, MS, of the VA Medical Center in White River Junction, VT, and H. Gilbert Welch, MD, MPH, of the Dartmouth Institute for Health Policy & Clinical Practice in Hanover, NH, reported a doubling in the incidence of thyroid cancer from 1975.
In this update published in JAMA Otolaryngology-Head & Neck Surgery, Davies and Welch analyzed trends in thyroid cancer diagnosis and mortality from 1975 to 2009 using data from nine regions in the Surveillance, Epidemiology, and End Results (SEER) program and information from the National Vital Statistics System.
Results revealed an increase in incidence from 4.9 to 14.2 cases per 100,000 individuals from 1975 to 2009 (relative risk [RR], 2.9; 95% CI: 2.71-3.1), with the researchers noting that more than half of cases occurred during the 7 years since the 2006 study.
Study data also showed that women were disproportionately affected by the increase. Compared with men, in whom the incidence of thyroid cancer doubled (RR, 2.2; 95% CI: 1.9-2.6), women experienced a tripling in incidence from 1975 to 2009 (RR, 3.3; 95% CI: 3.0-3.6). Additionally, in women, the absolute increase of 14.9 per 100,000 was nearly four-fold higher than in men (3.8 per 100,000).
Trends also indicate a shift toward detection of smaller lesions, according to the researchers. In 1988 to 1989, only 25% of tumors were 1 cm or smaller and 42% were larger than 2 cm. In contrast, from 2008 to 2009, 39% of detected tumors were 1 cm or smaller and 33% were larger than 2 cm.
The thyroid cancer mortality rate, however, remained stable from 1975 to 2009 (about 0.5 deaths per 100,000 individuals).
“We found that there is an ongoing epidemic of thyroid cancer in the United States,” Davies and Welch wrote. “It does not seem to be an epidemic of disease, however. Instead, it seems to be substantially an epidemic of diagnosis…Our findings demonstrate that the problem is due to the overdiagnosis of papillary thyroid cancer, an abnormality often present in people who never develop symptoms from it.”
As potential solutions to the issue, Davies and Welch propose three approaches. For one, they suggest presenting patients with randomized clinical trial data on active surveillance of small, asymptomatic cancers that were discovered incidentally to allow them to decide whether they want to pursue treatment. A second option could be to reclassify small, incidental thyroid neoplasms using a term other than cancer. A third alternative involves studying “patient-level patterns of care and thyroid cancer risk factors that result in a thyroid cancer diagnosis.”
But Davies and Welch also emphasized that the “upstream step of identification” is important.
“Physicians’ thresholds to palpate, image, and biopsy the thyroid have likely fallen too far,” they wrote. “Clinicians need more than trial results; they also need to be asking themselves whether they are looking too hard for thyroid cancer. Patients—and in the case of thyroid cancer, particularly women—need protection not only from the harms of unnecessary treatment but also the harms of unnecessary diagnosis.”
Barbara A. Burtness, MD
This important paper adds to the body of evidence that patients with small papillary thyroid cancers are being overtreated when thyroidectomy, radioiodine ablation, and aggressive thyroxine suppresion are used routinely. Other studies have shown that our interventions increase the incidence of leukemia and of cardiac death in thyroid cancer survivors.
This study nicely demonstrates that an enormous increase in thyroid cancer incidence, attributable to improved imaging and biomarker studies, has not led to any increase in thyroid cancer death.
An important research goal will be to develop imaging and histology criteria to identify patients who require only surveillance, but it is already clear that total thyroidectomy and radioiodine ablation should not be routinely employed in small papillary thyroid cancers.
Barbara A. Burtness, MD
Associate Director, Clinical Research
Professor, Department of Medical Oncology
Fox Chase Cancer Center