October 31, 2011 (Indian Wells, California) — A significant increase in the incidence of thyroid cancer in recent decades might be largely attributable to cancers incidentally found with ultrasound and other types of imaging, according to research presented here at the American Thyroid Association 81st Annual Meeting.
From 1975 to 2008, the incidence of thyroid cancer nearly tripled, increasing from 4.85 to 12.97 cases per 100,000. This increase is "more rapid than any other type of cancer," said coauthor Michael Malone, BS, a medical student at New York University Langone Medical Center in New York City.
Recent studies have suggested that increasing diagnostic scrutiny largely explains the apparent rise in cancers.
To evaluate the issue, Mr. Malone and his colleagues conducted a chart review of 404 patients who underwent initial surgery for well-differentiated thyroid cancer at the Langone Medical Center from January 2007 to August 2010.
They found that of 307 (76%) patients with stage 1 or 2 thyroid cancer, 46% had their tumors initially detected with an imaging study; the rest were detected because the patient or physician felt a mass in the neck.
Imaging studies were also the method of detection in 46 (47%) of the 97 (24%) patients with stage 3 or 4 well-differentiated thyroid cancer.
Among the tumors detected with imaging, 58% were less than 1 cm, 53% were 1 to 2 cm, 31% were 2 to 4 cm, and 39% were greater than 4 cm, Mr. Malone noted.
When tumors were detected with imaging, ultrasound was the leading modality, used in 104 (55%) patients, followed by computed tomography in 37 (20%) patients, magnetic resonance imaging in 19 (10%) patients, carotid duplex scan in 13 (7%) patients, and positron emission tomography or other imaging in 15 (8%) patients.
"It is important to note that these were sonograms that were not performed to evaluate something that was palpated on physical exam, but instead were performed for a variety of reasons, some appropriate and some not."
Patients whose tumors were detected with imaging were more likely to be male (32% vs 21%; P = .013) and were older (median age, 52 vs 46; P = .0004) than those whose tumors were detected without imaging.
The findings support the argument that imaging studies indeed heavily influence the rise in thyroid cancer incidence rates, Mr. Malone concluded.
"We feel that a substantial number of thyroid cancers are discovered by imaging rather than by palpation alone," he said. "This observation is true for small and large cancers, as well as early and advanced cancers."
"As with small cancers, the increasing incidence of larger and more advanced thyroid cancers may be the result of increasing diagnostic scrutiny and may not necessarily represent a true increase in disease," he observed.
- B. Ain, MD, professor of medicine and chair of cancer research at the University of Kentucky Medical Center, in Lexington, questioned whether the findings would hold true in a patient population outside of the New York City demographic.
"I think before you attempt to generalize, you should take into account the evidence of geography and different populations," said Dr. Ain.
"For example, the study deals with urban patients in population centers that have well-equipped medical centers, and many practitioners have unused ultrasound machines in their offices that have to generate money."
"In that situation, I assure you that you'll have a huge number of case findings by ultrasound and not by palpation," he said.
However, "if you take a rural population in eastern Kentucky, for instance, who have issues such as oxycontin use, smoking, and don't usually have ultrasound machines available, patients will generally present with palpable cancers and you will see the same increase in thyroid cancers among these patients as those in the big cities."
He added that some of the data used for this study have also shown that thyroid cancer has the "second highest increasing cancer death rate among all ages and all sexes, and to merely state this increased case finding and not account for the fact that these cases are killing more people despite with our advanced therapeutics makes it a little curious."
- G. Schuff, MD, of the Oregon Health & Science University in Portland, who moderated the session, said the study and the ensuing comments reflect a larger debate regarding the role of imaging in increasing thyroid cancer incidence rates.
"There are thyroidologists arguing on both sides of the issue," noted Dr. Schuff.
"Some say it's just imaging, others say it is a real increase, arguing that the increasing death rates indicate that this is not just an increase in 'small incidentally found' tumors. I don't think we have the answer to that particular question yet."
Mr. Malone, Dr. Ain, and Dr. Schuff have disclosed no relevant financial relationships.
American Thyroid Association (ATA) 81st Annual Meeting: Abstract 94. Presented October 28, 2011.
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