Imaging may be to blame for increasing incidence of thyroid cancer

Annual Meeting of the ATA

INDIAN WELLS, Calif. — Nearly half of all incidentally discovered well-differentiated thyroid cancers at a New York institution were detected on imaging studies, according to new data.

"Between 1975 and 2008, the incidence of thyroid cancer has increased from 4.85 cases per 100,000 to 12.97 cases per 100,000," Michael K. Malone, BS, a third-year medical student at New York University Langone Medical Center, said during a presentation. "It has been shown by Davies and Welch that 87% of these are papillary cancers under 2 cm and 49% are under 1 cm, suggesting that increasing diagnostic scrutiny is responsible for this and may represent subclinical disease."

Malone pointed out, however, that the incidence of larger cancers is rising as well. The intent of this study, he said, was to further investigate the role of imaging in detection of thyroid cancer. He and colleagues therefore conducted a retrospective chart review of patients with thyroid cancer seen at their medical center between 2007 and 2010. They collected data on method of initial detection; size and stage of cancer; and whether or not the tumor was palpable on initial examination by the operating surgeon.

The study population was comprised of 404 patients ranging in age from 11 to 86 years (median, 49 years), according to Malone. Of the cancers detected, 95% were papillary, 3% were Hurthle cell and 2% were follicular. Results revealed that 47% of cancers were initially detected by imaging and 53% by physical exam. Those whose cancers were detected via imaging were more likely to be men (32% vs. 21%; P=.013) and older (mean age, 52 years vs. 46 years; P=.0004) when compared with patients whose cancers were identified through physical exam only.

Regarding size, cancers smaller than 1 cm were more likely to be found on imaging, whereas those larger than 2 cm were more likely to be found upon physical exam. However, detection was equal for tumors measuring 2 cm in size, Malone said. Further breakdown in tumor size showed that 58% of cancers smaller than 1 cm; 53% of those between 1 cm and 2 cm; 31% of those between 2 cm and 4 cm; and 39% of those larger than 4 cm were found through imaging.

Among the 188 patients with cancers initially detected on imaging, 55% were found on sonogram, 20% on CT, 10% on MRI, 7% on carotid duplex scan and 8% on PET or other imaging studies.

"It is important to note that this sonogram was not performed to evaluate nodule palpation," Malone said. "It is also interesting to note that, while this does not relate to detection of cancers, a number of cancers that were diagnosed on imaging were indeed palpable by time of evaluation by the operating surgeon."

The researchers also reported that 46% of the 307 patients with stage I or II well-differentiated thyroid cancer and 47% of the 94 patients with stage III or IV disease were among those whose tumors were identified on imaging.

"We feel that a substantial number of cancers were discovered by imaging rather than by physical exam alone," Malone said. "This is both true for small and large cancers, and early and advanced stage cancers. As with small cancers, the increasing incidence of larger thyroid cancers may be the result of increasing diagnostic scrutiny and may not represent a true increase." - by Melissa Foster

For more information:

Malone MK. Oral 94. Presented at: the 81st Annual Meeting of the American Thyroid Association; Oct. 26-30, 2011; Indian Wells, Calif.

Disclosure: Mr. Malone reports no relevant financial disclosures.

This presentation was particularly interesting because of the fact that, when the researchers looked at what size the tumors were detected by imaging, they did not just find small tumors, which we thought would otherwise not be palpable, but they also found that larger tumors were identified by imaging rather than by palpation. So, this kind of muddies the waters even further in terms of what is really going on in terms of the increasing incidence of thyroid cancer and whether that's supported just by increasing incidental findings. The findings do corroborate an increasing incidence in thyroid cancer. However, what wasn't brought out in this particular presentation, but has been shown in other studies, is that there's also an increasing death rate from thyroid cancer, which lends credence to the fact that this is not just detection bias and bias-related imaging techniques.

- Kathryn G. Schuff, MD
Oregon Health and Sciences University
- John A. Copland, PhD
Mayo Clinic

Disclosure: Drs. Copland and Schuff report no relevant financial disclosures.

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