TUESDAY, May 9, 2006 (HealthDay News) -- The apparent upsurge of thyroid cancer cases in the United States is the result of better, high-tech diagnostic tests that are picking up minuscule tumors -- most of which pose no long-term threat, a new study says.
"New tests are available to detect abnormalities we never saw in the past," said the co-author of the national report, Dr. Louise Davies, an assistant professor of surgery at Dartmouth Medical School.
The thyroid is a butterfly-shaped gland located beneath the voice box that produces thyroid hormone, which the body uses to regulate growth and metabolism.
The reported number of thyroid cancers more than doubled from 3.6 per 100,000 Americans in 1973 to 8.7 per 100,000 in 2002 -- about 24,000 newly diagnosed thyroid cancers nationwide, according to the report in the May 10 Journal of the American Medical Association. But that 2.4-fold increase was not accompanied by a rise in deaths from the condition; deaths have remained stable at just 0.5 per 100,000, the researchers said.
The findings should help settle controversy around rising thyroid cancer rates. Some investigators have attributed the increase to environmental radiation from sources such as nuclear power plants. However, the real reason may be "increased detection of subclinical disease," the report said.
Ultrasound scans and needle biopsies can detect nodules as small as 2 millimeters, a quarter of the size of a pencil eraser. Until the new techniques came along, doctors were detecting much larger nodules, 1.5 centimeters or more, explained Davies, who's also a member of the outcomes group at the Department of Veterans Affairs Medical Center in White River Junction, Vt.
Data from the U.S. National Cancer Institute's surveillance system showed that nearly half the tumors detected during the study period were 1 centimeter or less, she said.
Most of those cancers grow so slowly they pose no threat to life, Davies said. "People should know that nodules are common and that there is a lot more thyroid cancer out there than really matters," she said.
The situation with thyroid cancer is similar to that with prostate cancer. In both cases, autopsies have shown that a fair number of people, perhaps 5 percent, have cancers that were not detected.
"Some of these [thyroid and prostate tumors] are so small and grow so slowly that they would not be evident during the lifetime of the patient," said Dr. Michael Tuttle, acting chief of the endocrinology service at Memorial Sloan-Kettering Cancer Center in New York City.
But the experts agreed that the detection of such small cancers presents a dilemma for physicians.
"We need to start considering how aggressively we should treat these tumors," Davies said. "I think it is something people are struggling with."
"We're always looking for the needle in the haystack," Tuttle said. "In the worst-case scenario, we end up overtreating a good number of patients."
But overtreatment might be necessary out of fear of missing the few small cancers that will grow aggressively and become life-threatening, he said. As in prostate cancer, there is no way now to identify which thyroid growths can be safely left alone and which require surgery, Tuttle said.
"This is a problem we are going to have to deal with," he said. "I don't think it will change in my lifetime."
But while the new report highlights a dilemma for doctors, it does offer comfort to the public, Tuttle said. The important thing for patients is that we don't have an epidemic of thyroid cancer, he said.
For more on thyroid cancer, head to the U.S. National Cancer Institute.