Patients whose thyroid cancer was detected as an incidental finding tend to be older and have later-stage disease -- although tumor size and metastases aren't much different from thyroid cancer diagnosed clinically, researchers found.

That suggests the rise in thyroid cancer seen over the last few decades isn't solely attributable to an increase in incidental findings, David Goldenberg, MD, of Hershey Medical Center in Pennsylvania, and colleagues reported online in JAMA Otolaryngology -- Head & Neck Surgery.

"If heightened diagnostic scrutiny was causing the increased incidence of thyroid cancer, one would expect incidentally discovered thyroid cancers to be smaller and less advanced in stage at the time of presentation," they wrote. "Nonetheless, it is difficult to ignore the contribution of advanced imaging techniques and the increased use of diagnostic studies on the discovery of incidental thyroid nodules."

The incidence of thyroid cancer has nearly tripled over the last 30 years, from about five cases per 100,000 in 1975 to nearly 15 per 100,000 in 2009, according to data from the Surveillance, Epidemiology, and End Results registry.

Some researchers have attributed the rise to the improved sensitivity of diagnostic techniques and imaging modalities, while others argue that it's a true increase, potentially due to some lifestyle or environmental factor.

To compare incidentally discovered thyroid cancer with cancer diagnosed normally, Goldenberg and colleagues conducted a retrospective review of medical records from 238 patients at their hospital -- 31 of whom had incidentally discovered thyroid cancer, and 207 who were diagnosed normally.

They did find a significant difference in age between the groups, with the incidentally discovered cancer group being older (mean age 56.4 versus 41.8, P<0.001) -- which could reflect the fact that use of medical services rises with age, they noted.

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