A new study hints that the incidence of diagnosed thyroid cancer in the United States — which has been increasing rapidly over the past 30 years — might be leveling off, perhaps because of more conservative recommendations about which nodules to biopsy and changing practice patterns.
But experts not involved in the study say it might be too soon to draw firm conclusions on changing trends.
The study, by Luc G.T. Morris, MD, from the Memorial Sloan Kettering Cancer Center in New York City, and colleagues, was published online April 14 in JAMA Otolaryngology–Head & Neck Surgery.
The team analyzed the incidence of thyroid cancer in the United States from 1983 to 2012 using the Surveillance, Epidemiology, and End Results (SEER) registry of the National Cancer Institute.
They found that from 1988 to 1998, the incidence of thyroid cancer rose by 3% annually. From 1998 to 2009, the trend accelerated to 6.7%, but then stabilized to 1.75% from 2010 to 2012. "The stabilization in incidence rates from 2010 to 2012 remained when tumors were stratified by size, and was most pronounced for tumors of subcentimeter size," the researchers report.
"Epidemic of Diagnosis"
"Over the past 30 years, the incidence of thyroid cancer in the United States has tripled," Dr Morris noted in email to Medscape Medical News. "It used to be a mystery why this was happening. But recently, many researchers have shown that this is mainly happening because of improvements in medical technology that allow us to better identify and biopsy small nodules in the thyroid gland."
Many of these small nodules do turn out to be thyroid cancers, Dr Morris reported. "In fact, up to 30% of healthy people have small cancers in their thyroid glands, and nearly all of these would not go on to cause any problems for the person if the cancer were never discovered. In other words, a large reservoir of small thyroid cancers has always been present, like a huge submerged iceberg, but we are just getting better at finding them," he explained.
"Therefore, the dramatically rising incidence of thyroid cancer is best characterized as an 'epidemic of diagnosis,' not an epidemic of disease. This is highly relevant to patients found to have these small thyroid cancers, because it means that many of these cancers would not have caused problems for the patient, and that there would be no benefit (only potential harm) to diagnosing and surgically removing them," Dr Morris said.
In the past few years, there has been greater awareness of this, he noted, and thyroid cancer specialists have begun to recommend that physicians be "more selective" about investigating and biopsying small thyroid nodules, he pointed out.
In 2009, the American Thyroid Association (ATA) recommended that thyroid nodules smaller than 0.5 cm need not be biopsied. In 2015, the ATA updated their recommendation, saying that nodules smaller than 1 cm and not all nodules larger than 1 cm need to be biopsied.
Dr Morris said the apparent leveling off of the incidence of thyroid cancer noted in the study "has occurred at the same time as clinical practice guidelines have begun to urge less aggressive investigation of small thyroid nodules. We infer, but cannot prove, that the leveling off may be due to changes in physician practices."
Too Soon to Say for Sure
However, Juan Brito Campana, MBBS, an endocrinologist at the Mayo Clinic in Rochester, Minnesota, urged caution in interpreting the data.
"It is true that, after 2009/2010, it seems that the rapid increase in thyroid cancer incidence at least has plateaued, compared with the trend that was happening before, so this is a valid assessment and it is good to bring this to the field," he told Medscape Medical News.
However, "because it is based on such a short period of time, you cannot actually conclude that it is true. To assess a trend, a change in the incidence rate, 2 years is too short. For example, back in 1990, the incidence also plateaued, and then after 2 or 3 years of being stable, it increased rapidly. So you cannot really make a robust conclusion based on just 2 years of data," Dr Campana noted.
Amanda M. Laird, MD, a surgeon in the comprehensive thyroid program at the Montefiore Einstein Center for Cancer Care and assistant professor of surgery at the Albert Einstein College of Medicine in New York City, also thinks it might be "a little early" to conclude that the incidence of thyroid cancer is leveling off, because the most recent ATA guidelines only came out in the past few months. "We may need a little more distance on the publication of the most recent guidelines, and see what happens in the next 5 to 10 years," she told Medscape Medical News.
Dr Morris noted that the SEER registry data "mirror recent events in South Korea, where the incidence of thyroid cancer increased even more dramatically (15-fold in 10 years) because of widespread ultrasonography screening. Concerned physicians appealed to the public about overdiagnosis of small thyroid cancers, leading to a dramatic reversal and an actual drop in thyroid cancer diagnoses. We anticipate that a similar course correction may be beginning to occur in the United States," Dr Morris said.
JAMA Otolaryngol Head Neck Surg. Published online April 14, 2016. Abstract
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