The number of people diagnosed with thyroid cancer is growing at an unprecedented rate and medical researchers don’t know why. Thyroid cancer increased at a rate of 6.5 percent a year from 1997-2006 making it the fastest increasing cancer among women and men, according to recently released National Cancer Institute data. Over that same period, prostate, breast, lung and colon cancer rates decreased. The 2006 data is the most recent data available; the three-year lag represents the time it takes researchers to compile the statistics.
Experts can only speculate about what is causing a change in the thyroid cancer rate.
“We’re all concerned about this increase,” said Dr. Elaine Ron, a senior investigator at the National Cancer Institute. “We have set up a thyroid cancer working group to see what studies we’re already doing on thyroid cancer, what studies can we do to try and find out more about this increase, but at the moment we can’t really tell you.”
The thyroid, a butterfly-shaped gland that sits at the front of the neck just above the breastbone and overlying the windpipe, produces hormones responsible for controlling heart rate, blood pressure, metabolism and childhood growth and development.
There were approximately 410,000 men and women alive in the United States who had a history of thyroid cancer, as of Jan. 1, 2006. The American Cancer Society predicted more than 37,000 new cases of thyroid cancer were diagnosed in 2008, up from about 17,000 in 1999.
The good news is that thyroid cancer is highly treatable. The mortality rate has remained stable at .5 percent per year meaning about 1,500 people die annually from thyroid cancer.
As the reports of thyroid cancer increased over the past two decades, some experts said the increase was simply because of better diagnostic procedures. For instance, detection methods such as ultrasonography now allow doctors to diagnose thyroid cancer nodules smaller than 1 centimeter.
In their Journal of the American Medical Association article published on May 10, 2006, Dr. Louise Davies and Dr. H. Gilbert Welch wrote the detection of more “subclinical disease,” skewed the thyroid cancer rate. They wrote the increasing rate was “not an increase in the true occurrence of thyroid cancer,” but rather better detection allowed doctors to diagnose cancer that previously would have gone undetected.
Fast forward three years – new research proves there is more to the story than better detection.
More than better detection
Dr. Kenneth Burman, the chief of Endocrinology at the Washington Hospital Center and the current president of the American Thyroid Association, said his understanding and best guess is the increased frequency of thyroid cancer may be in large part related to detection, but it also represents some type of biologic change in the disease prevalence.
“Whether those represent environmental factors, such as radiation exposure, or genetic factors, no one knows,” Burman said. A new study analyzing National Cancer Institute data proves some unknown factor is contributing to the increasing rate of thyroid cancer. "It’s not just improved medical surveillance and diagnosis,” Ron said.
She came to that conclusion based on her review of the Institute’s Surveillance Epidemiology and End Results data. The data includes information on cancer incidence, mortality, survival, prevalence and lifetime risk statistics as well as the type and size of tumors reported.
The study focused on papillary cancer – the most common type of thyroid cancer – because that’s the type of tumor experts say is increasing consistently among all racial and ethnic groups.
“We’re seeing an increase in the larger tumors and also in tumors of regional stage, so it’s not just the very small, early tumors,” Ron said.
The increase in the number of tumors larger than 2 centimeters, and even 5 centimeters, suggests there is more to the increasing rate than better diagnostic procedures.
According to Ron, local stage and smaller tumors are generally picked up during image screening. In contrast, regional stage and larger tumors are generally diagnosed clinically during a physical exam of the neck.
Because of the increase in larger tumors, image screening can no longer be pointed to as the sole reason more thyroid cancers are being reported, Ron said.
The study – authored by researchers from the Institute, Walter Reed Medical Center and Brooke Army Medical Center – was published in the March issue of Cancer Epidemiology and Biomarkers and Prevention. Ron’s team analyzed data from 1980 to 2005.
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