Rise in thyroid cancer may be tied to radiation, diet

A medical mystery: As overall cancer rates fall, why are thyroid cancer rates rising? Diagnoses of cancer in this gland in the neck are increasing about 6 percent a year, faster than cancers found anywhere else, according to one National Cancer Institute analysis.

Researchers know one big reason: The many medical scans Americans have, for everything from neck pain to artery plaque, are turning up thousands of tiny thyroid tumors that otherwise might go undetected and often would do no harm.

"We call them 'incidentalomas,' " says Amy Chen, a head and neck surgeon at Emory University in Atlanta and American Cancer Society researcher.

But that's not the whole story. Two recent studies, including one co-written by Chen, show larger thyroid tumors are being found at an increasing rate, too. And those can't be explained by more aggressive diagnosis alone, researchers say.

"There is something else going on" to contribute to the 37,000 cases of thyroid cancer expected this year, Chen says. That's up from 18,000 in 2000.

What is that "something else"? In-depth research on that is just starting, says Elaine Ron, a senior investigator at the cancer institute. The good news, she says, is that 98 percent of those with the most common forms of the cancer live at least five years. Overall death rates are not rising. But it's important to study the rise in cases, she says: "This is a large increase, and it's been going on for a long time. If there's a biological reason, we can try to prevent it."

Among factors researchers are considering:

Radiation: Researchers know radiation exposure, especially in childhood, can increase thyroid cancer risk. They don't know whether increased radiation exposure from medical scans and other sources is contributing to the overall increase.

Obesity: Some early studies suggest it might be a factor — and researchers know it's increasing.

Diet: Some studies suggest diets low in fruits and vegetables or with iodine levels that are too high or too low might play roles.

Watching the research: Caroline Stetler of Washington, D.C. Stetler, 28, had thyroid cancer at 16. As a grad student at American University's Investigative Reporting Workshop, she researched the cancer and was shocked by the numbers.