Thyroid cancer rates double in a decade

Washington -- Thyroid cancer rates have doubled in the past 10 years, and the increase has been the greatest among women. But why this jump is happening is unknown.

The rate of newly diagnosed thyroid cancer has surpassed the rate of ovarian cancers found, said Steven Libutti, MD, chief of the National Cancer Institute's tumor angiogenesis section. "I think it has moved up to No. 7" in the most common cancers among women, he said. "Ten years ago, it did not even make the top 10 list."

Theories abound as to why. They range from radiation exposure -- either via the environment or as a result of its use as a treatment tool -- to physicians' sharpened detection skills. Recent research also suggests that a female sex hormone, most notably estradiol, could play a role.

Physicians are urged to be vigilant because, if detected early and treated optimally, thyroid cancer has an excellent cure rate, Dr. Libutti said.

The "Annual Report to the Nation on the Status of Cancer" released in September tracked this cancer's increase among women since 1981 and found that it rose by 2.2% per year until 1993, then began a 4.6% annual increase that lasted until 2000. From 2000 to 2003, this rate nearly doubled again to 9.1% per year.

Rates among men have also been escalating, noted Ahmedin Jemal, PhD, the American Cancer Society's strategic director for cancer occurrence. In 1990, incidence rates for men were 2.9 thyroid cancers for every 100,000 people. By 2003, the rate was 4.6 cases per 100,000, a nearly 50% boost. During the same period the rate for women went up by 75%, he said.

"These rising trends are likely explained in part by changes in medical surveillance, but may also be a result of changes in risk factors," the cancer report concluded.

The theory that better detection is the cause was explored in a May 10 article in the Journal of the American Medical Association. The researchers concluded that thyroid cancer's increasing U.S. incidence reflected better detection of subclinical disease that likely would never become a life-threatening cancer.

Dr. Libutti finds it a stretch to attribute the disease's growth to better vigilance and detection alone. Improved detection wouldn't account for the higher increase among women, he said -- both men and women have thyroid glands. And there is no mass screening campaign for thyroids like mammography for breast cancer that could account for the rise in numbers. Although risk awareness has increased, especially during the past five years, and more people may be getting checked, "I don't think it would account for doubling in the last 10 years."

Due diligence

Primary care physicians might want to ask a few more questions to ascertain risk for thyroid cancer, suggested Kenneth Burman, MD, chief of the endocrine section at Washington Hospital Center in Washington, D.C. Inquiries could be made about trouble swallowing, hoarseness or neck pain.

Family history is also a factor. "It has recently become known that if there is a history of thyroid cancer, the likelihood of another relative getting it is much higher," he said.

Physicians also should ask about past radiation treatments. Low-dose radiation was used to treat enlarged tonsils in the 1940s and '50s and acne in the early '60s. Radiation for treating Hodgkin's lymphoma and cancers of the neck was administered decades ago without protective shields and is a suspected contributor to today's thyroid cancer increases. Exposure to fallout from the Chernobyl nuclear power plant explosion 20 years ago in the former Soviet Union is another well-recognized risk factor.

Detection normally occurs with the discovery of a nodule during an examination. Incidental detection when a patient has a neck study, perhaps a carotid artery scan, also could yield a snapshot of a thyroid nodule that should be investigated, Dr. Burman said. "An incidentally discovered nodule is no more or no less likely to harbor thyroid cancer."

Suspicion should be heightened when a nodule is larger than 1 cm to 1.5 cm in any dimension, and such nodules should be aspirated, according to the thyroid association's guidelines. But the presence of more worrisome characteristics should trigger increased vigilance even with smaller nodules, Dr. Burman wrote in editorial in the June Journal of Clinical Endocrinology & Metabolism.

To put thyroid cancer in perspective, even though its rate of detection is increasing, the numbers of diagnosed patients still fall well below those with other cancers. In the United States, there are roughly 150,000 to 160,000 new colon cancer cases each year, about 210,000 new breast cancer cases and between 180,000 and 190,000 lung cancer cases. For thyroid cancer, totals are about 22,000 new cases each year in women and about 7,000 each year in men, Dr. Libutti said.

In order to zero in on the worrisome nodules and separate them from harmless growths, work is under way to find better ways to distinguish between them without aspiration. For example, Dr. Libutti's research focuses on improving diagnosis. "We've been developing genomic- and proteomic-based diagnostics to help distinguish benign nodules from cancer," he said.

Research also was presented Oct. 12 at the American Thyroid Assn.'s annual meeting in Phoenix on the identification of a biomarker. Researchers from Memorial Sloan-Kettering Cancer Center in New York City used mass spectroscopy to identify a thyroid cancer-specific serum peptide profile that was able to correctly identify samples with 95% sensitivity and specificity.

"This serum peptide profile has the potential to serve as a molecular fingerprint that distinguishes metastatic thyroid cancer from normal healthy patients, allowing physicians the ability to diagnose thyroid cancer earlier," said lead author Andrew J. Martorella, MD.