Although the U.S. Supreme Court has not indicated what type of thyroid cancer Chief Justice William H. Rehnquist has, some experts in the field said they hope news of his illness will spark interest in finding new treatments for the rarest and deadliest forms of the disease.

Anaplastic thyroid cancer accounts for just 1 to 2 percent of cases, but patients with that type often die within months of diagnosis. Doctors not involved in Rehnquist's medical care speculated Monday that the chief justice's announcement that he is undergoing radiation and chemotherapy treatment, following a tracheotomy, suggests he may have that form. The deadlier anaplastic cancer usually occurs in patients 65 or older; Rehnquist is 80.

"So far they have not done surgery to remove the thyroid," the standard treatment, said James A. Fagin, director of the division of endocrinology at the University of Cincinnati, "suggesting that it is probably not possible to remove it. . . . Then you're just left with the combination therapy with both external radiation and chemotherapy." Because these treatments aren't commonly used for other forms of the disease, he said, he'd concluded the cancer was likely anaplastic.

Research advances in anaplastic thyroid cancer have been stymied by the fact that most thyroid cancers are easily treated and rarely fatal, experts say.

Thyroid cancer "hasn't received the support for research that many other cancers have, [because] it's perceived to be one of the most treatable cancers," said Paul Ladenson, director of the Johns Hopkins Thyroid Tumor Center in Baltimore and president of the American Thyroid Association.

"If you had a treatment [for most thyroid cancers] that involved massive surgery or very intensive, very toxic chemotherapy, everyone would be looking for new treatments," said Paul Wallner, a former thyroid cancer specialist at the National Cancer Institute (NCI) who is now senior vice president of 21st Century Oncology, a firm that owns and operates radiation oncology centers. "But what you've got is . . . a tumor where, for the most part, 90 percent of individuals do quite well."

About 23,600 people in the United States will be diagnosed with thyroid cancer this year, according to the American Cancer Society (ACS). About 1,460 people will die from the disease. By comparison, ACS estimates that there will be 217,440 new breast cancer cases this year and 40,580 deaths. About 230,110 people will be diagnosed with, and 29,900 will die from, prostate cancer. Ladenson said the incidence of thyroid cancer is rising faster than any other cancer.

Eighty to 90 percent of thyroid cancer diagnoses are for papillary and follicular cancers, according to NCI. Most patients with these forms are cured with thyroidectomies -- removal of all or part of the thyroid -- and, often, radioactive iodine therapy. Most cancers are found when doctors or patients notice a lump, or nodule, on the thyroid, the butterfly-shaped gland at the base of the neck that produces hormones regulating heart rate, body temperature and energy level. The lumps are relatively common, clinicians said, and must be evaluated to rule out cancer. About 4 percent of all people have these lumps, but only 5 to 10 percent of these nodules are cancerous.

The lumps are often detected during routine physical exams, clinicians said, or when a patient notices a small bulge in his neck. Common symptoms include hoarseness, pain in the throat or neck, difficulty swallowing or breathing and swollen lymph nodes in the neck or elsewhere. But some thyroid cancers have no symptoms.

The Oct. 25 announcement that Rehnquist had undergone a tracheotomy "in connection with a recent diagnosis of thyroid cancer" suggests he may have a tumor pressing on his windpipe, or trachea, or that his cancer has spread to the nerves in his voice box, doctors said.

Despite its grim outlook, no new treatments are in the works for the anaplastic form, mostly because only a small number of patients develop this type.

"We need new, more accurate diagnostic tests, said Ladenson, who would not comment specifically on Rehnquist's condition. "We need new therapies to treat patients with advanced thyroid cancer more effectively, and we need more funding."

Another less treatable form, medullary thyroid cancer, affects about 5 to 10 percent of patients and often runs in families. Like the anaplastic type, medullary thyroid cancers often spread quickly -- most commonly invading nearby lymph nodes, nerves and blood vessels, making them difficult to treat and the prognosis bleak.

Those at greatest risk for thyroid cancer include people with a family history of the disease, those who don't have enough iodine in their diets (sources of iodine include iodized salt, milk products and seafood, among others) and those who have been exposed to high amounts of radiation, according to NCI. Other risk factors include being female, white or older than 40. Patients who know medullary thyroid cancer runs in their families can have genetic testing done to determine whether they have a gene alteration that puts them at greater risk.

"If you have the [gene] mutation, your chances of getting it are very high," Fagin said. The test costs about $1,000, Fagin said, and is usually covered by insurance.

Blood work to check thyroid hormone levels is often the first diagnostic step. If hormone levels are high, the patient may have hyperthyroidism, or overactive thyroid, whose symptoms include fatigue, loss of appetite, nausea and increased thirst. If those levels are low, the patient may have hypothyroidism, or underactive thyroid, marked by weakness, fatigue, unintentional weight gain and hoarseness, among other symptoms. Both are benign conditions that require medication to regulate hormone levels.

But if the patient's blood work is normal, doctors may order an ultrasound or a thyroid scan to determine the makeup of the thyroid nodule. The lumps can be cystic (made of fluid and less likely to be cancerous) or solid (made of live tissue and more likely to be malignant).

Ultimately, doctors often recommend a fine needle aspiration -- a biopsy done in the doctor's office using a thin needle inserted directly into the lump -- or a surgical biopsy so that tissue can be drawn and analyzed in a lab. When these tests are inconclusive, the doctor may repeat the biopsy, or simply remove the thyroid as a precaution.

Patients whose thyroids are wholly removed must take thyroid hormone replacement medications for the rest of their lives.

Ladenson said increased "molecular diagnostic testing" -- which doctors do not use in standard treatment today -- could help clarify biopsies, keeping patients from having unnecessary surgery. The testing would confirm a thyroid tumor is not cancerous, he said, by identifying changes in structure that are unique to malignant tumors. It could also help scientists ultimately develop drugs to treat them. But the test, conducted on a tissue sample drawn during a biopsy, is not definitive, Ladenson said, because it may fail to identify some patients who do have cancer.

Some researchers are doing early stage work examining the genetics of thyroid cancer. They hope it will lead to an effective way to treat the more deadly forms of the disease and recurrences in previously treated patients.

"The research that's being done is very analogous to the research that's being done on many different other forms of cancer, which is to take advantage of our knowledge about the genetics of these cancers to target" genetic abnormalities in thyroid cancer cells, Fagin said. The treatment -- called targeted therapy -- uses drugs to "hit the cancer cell and leave other tissues relatively unscathed," Fagin said.

This therapy could be especially promising for medullary thyroid cancers, since it often runs in families. But this type of therapy would be difficult to study in anaplastic cases.

"In anaplastic [thyroid cancer], the disease tends to progress so rapidly that this hasn't been practical," said Wallner, adding that targeted therapies require a lot of time and effort and that the small number of anaplastic patients makes it more difficult to study than other cancers. "If it's your disease, that's critically important. But from the perspective of research, it's not practical."

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The thyroid, at the neck's base,

can be subject to cancers, most treatable.