What Is It?
Thyroid cancer is the uncontrolled growth of abnormal cells in the thyroid gland. The thyroid gland is shaped like a butterfly and is located under the Adam’s apple in the front of the neck. Most cases of thyroid cancer are cured.
The thyroid has two types of cells that produce two hormones that help to regulate body functions.
- Follicular cells in the thyroid produce a hormone called thyroxine, or T-4, which controls the body’s rate of metabolism. Metabolism is the breakdown of complex molecules to release energy for the body, as well as the buildup of cells and tissues from simpler molecules.
- C-cells, also called parafollicular cells, produce calcitonin, a hormone that regulates body levels of calcium and phosphate.
There are five types of thyroid cancers:
- Papillary carcinoma (also known as papillary adenocarcinoma) — This is the most common type of thyroid cancer, accounting for 75 percent of all thyroid cancers. It develops from follicular cells and usually grows slowly. In most cases, it is in only one of the thyroid gland’s two lobes, but it affects both lobes in 10 percent to 20 percent of patients. Papillary carcinoma often spreads to nearby lymph nodes in the neck.
- Follicular carcinoma — This is an uncommon thyroid cancer that is believed to originate in the follicular cells. Only about a third of these tumors are cancerous.
- Hürthle cell neoplasm (follicular adenocarcinoma) — This is the second most common type of thyroid cancer, and it originates in follicular cells. Although this type of cancer usually involves only the thyroid gland, it sometimes can spread to other body areas, especially the lungs and bone.
- Anaplastic carcinoma (undifferentiated thyroid cancer) — This is the rarest form of thyroid cancer, and it has the worst prognosis. Scientists believe that it develops from existing papillary or follicular carcinoma. Anaplastic carcinoma is aggressive, and spreads quickly to the neck and other parts of the body.
- Medullary thyroid carcinoma (MTC) — This is the only type of thyroid cancer that develops from the thyroid’s C-cells. MTC is not associated with prior radiation exposure. It can spread to the lymph nodes, the lungs and the liver even before a thyroid nodule (abnormal lump in the thyroid) has been detected. MTC produces the hormone calcitonin, as well as a protein called carcinoembryonic antigen (CEA). Both of these chemicals are released into the blood. MTC can be either sporadic or familial. Sporadic MTC (80 percent of all MTC cases) is not inherited and usually develops in only one thyroid lobe. Familial MTC (20 percent of cases) has two forms, each of which can affect several generations of the same family.
In very rare circumstances, tumors arising from connective tissue (sarcomas) and lymph nodes (lymphomas) also can start in the thyroid gland. These are treated differently from other thyroid cancers.
Although scientists have not identified the exact cause of thyroid cancer, some studies have shown that people exposed to nuclear fallout or nuclear power-plant accidents have a higher risk of developing thyroid cancer. People who have received high-dose radiation for acne or swollen adenoids as a child are at increased risk. The incidence of thyroid cancer also is higher in countries where diets are low in iodine. In addition, people with certain medical conditions, such as Cowden’s disease and familial polyposis have a higher risk of developing thyroid cancer.
Some forms of thyroid cancer are inherited. These occur alone (inherited medullary thyroid cancer) or as part of a familial cancer syndrome known as multiple endocrine neoplasia (MEN) type 2. Patients with MEN-2, which is further subdivided into MEN-2A and MEN-2B, develop tumors in other organs such as the adrenal gland (pheochromocytomas) and peripheral nervous system (neuromas and ganglioneuromas).
Recent scientific studies also indicate that mutations (alterations in inherited gene segments of DNA) may cause some forms of thyroid cancer. For papillary carcinoma and MTC, DNA mutations may involve the ret oncogene (a gene that promotes cell division). In anaplastic carcinoma, mutations of the tumor-suppressor gene p53 may be present.
Thyroid cancer is rare, accounting for only about 1.5 percent of all types of cancer. This cancer strikes about 18,000 people in the United States each year, and causes more than 1,200 deaths. The illness is more common in women than in men.
Some common symptoms that can be caused by thyroid cancers include:
- A pain in the neck that may shoot up into the ears
- A lump in the neck that may or may not grow rapidly
- Difficulty swallowing
- Difficulty breathing
- A persistent cough
It is important to recognize that some of these symptoms are also present in conditions other than cancer.
During the physical exam, your doctor will take your pulse rate and blood pressure. A rapid pulse and high blood pressure may indicate that you have high levels of thyroid hormone in the blood, a condition called hyperthyroidism. Your doctor also will feel your neck to evaluate the size and firmness of the thyroid, to check for any thyroid lumps and to document the presence of any enlarged lymph nodes. To help diagnose thyroid cancer, your doctor also may order the following tests:
- Fine-needle aspiration (FNA) of a thyroid nodule — When your doctor has found a thyroid nodule in your neck, this procedure is considered to be the most effective diagnostic test for thyroid cancer. It usually can be performed in your doctor’s office. A local anesthetic is injected to numb the skin over the thyroid nodule. Then the doctor inserts a thin needle into the thyroid nodule and withdraws cells and fluid. These are sent to the laboratory and examined under a microscope for signs of cancer. In 60 percent to 80 percent of FNA procedures, laboratory examination shows that the nodule is not cancerous (benign). About 5 percent of cases are diagnosed as cancer. The remaining 15 percent to 35 percent of cases are ruled suspicious, suggesting that cancer may be present.
- Serum thyroglobulin blood test — This test examines the overall condition of the thyroid gland, but it does not identify cancer specifically.
- Blood calcitonin test — This test is ordered if the doctor suspects MTC or if your calcium and phosphate levels are abnormal.
- Thyroid scan — In this test, a small amount of radioactive iodine or technetium either is swallowed or injected into a vein. The radioactive chemical will be taken up by the thyroid gland. A special camera is positioned next to your neck to measure the amounts of radioactive chemicals in the thyroid area. These scans can help doctors to determine whether a nodule in the gland is actively producing thyroid hormone. If it is producing the hormone, cancer is less likely. If you have thyroid cancer, this test may determine whether cancer has spread to other parts of your body, especially after the thyroid gland has been removed surgically.
- Thyroid ultrasound — In this test, sound waves are used to create images of the thyroid without using X-rays. A thyroid ultrasound may help to distinguish between cysts, cystic tumors and solid tumors.
- Computed tomography (CT) or magnetic resonance imaging (MRI) of the neck — CT is a modified X-ray beam that produces cross-sectional images of the thyroid area. MRI involves the use of large magnets and radio waves to produce cross-sectional, computer-generated images of the thyroid gland and nearby structures in the neck.
Thyroid cancer can develop slowly and remain undetected for years. Like other cancers, it will continue to grow and spread until treatment is provided.
Because many people develop thyroid cancer without having any known risk factors for the illness, this form of cancer is hard to prevent. However, new genetic blood tests can be used to identify people who have a high risk of developing the familial types of MTC. Once inherited MTC strikes one family member, all genetically related family members can be tested. Those who test positive, without showing symptoms of thyroid cancer, may elect to have the thyroid removed to prevent thyroid cancer. After surgery, these patients need to take thyroid hormones for the rest of their lives.
The American Cancer Society recommends that everyone older than 40 should have their thyroid examined during their annual routine physicals. This exam should be done every three years for people between the ages of 20 and 39.
Although a patient’s specific treatment plan depends on the type of thyroid cancer and how far it has spread, surgery is the main method used to treat thyroid cancer. A surgeon will remove all of the cancer, as well as all or part of the remaining thyroid and nearby lymph nodes.
Other important parts of the treatment plan may include:
- Thyroid hormone therapy — If the entire thyroid gland is removed surgically, thyroid hormone medication will help to restore normal metabolism and to suppress a pituitary gland hormone that can accelerate the growth of any remaining thyroid cancer cells. A person must take oral thyroid hormone tablets for life.
- Radioactive iodine treatment — In this treatment, radioactive iodine is used to kill any cancerous thyroid tissue not removed by surgery.
- chemotherapy — In this treatment, anticancer drugs are taken by mouth or injected into a vein. Side effects can include hair loss, nausea and vomiting. Chemotherapy is used to treat more aggressive forms of thyroid cancer and more advanced cancers.
- External beam radiation therapy — In this treatment, high-energy rays or particles are focused on the cancer to kill cancer cells.
Each treatment for thyroid cancer produces side effects that can linger for a few months. Follow-up care can continue for 20 to 30 years.
When To Call A Professional
Contact your doctor promptly if you discover a lump anywhere in your neck. Also seek medical help if you experience persistent neck pain, a persistent cough or any difficulty breathing or swallowing.
Thyroid cancer usually can be cured if it is detected early. There are more than 500,000 survivors of thyroid cancer in the United States. The prognosis for follicular and papillary cancers depends on the patient’s age, tumor characteristics, whether the cancer has spread, and whether the tumor was completely removed surgically. The prognosis for MTC depends on whether the cancer occurs without a known cause, is inherited alone, or is inherited as part of a cancer syndrome (MEN-2). Regular follow-up exams are critical, because 5 percent to 20 percent of patients will have the tumor come back.
Anaplastic carcinoma is nearly always fatal, with only 3 percent to 17 percent of patients surviving five years after diagnosis.
Diseases and Conditions Center
All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.