Thyroid cancer

Definition
Thyroid cancer is a disease in which the cells of the thyroid gland grow abnormally and form a cancerous tumor.

Anatomy
The thyroid gland is located in the neck, just below the voice box and on top of the windpipe. This butterfly-shaped gland produces thyroid hormones triiodothyronine (T3) and thyroxine (T4), which help regulate several body systems, including metabolism and the conversion of calories to energy. The thyroid hormones also help control body temperature, growth and skeletal development, heart rate and function, muscle tone and function, nervous system development, mental function and body weight.

Causes/associated factors
Although thyroid cancer can develop in people of all ages, it's most common in people over 40. The condition is about three times more common in women than men. Research has improved our understanding of how thyroid cells change and become cancerous, but the exact cause of thyroid cancer often remains unknown. As explained below, certain factors can increase the risk of developing thyroid cancer. Many people who have the condition have no known risk factors, however.

Types of thyroid cancer
Of the many types of nodules (small, rounded, solid masses of tissue) that can develop in the thyroid gland, about 5 percent are cancerous. Based on their appearance under a microscope, cancerous nodules are divided into four main types:
papillary
follicular
medullary
anaplastic
Papillary carcinoma accounts for 60 percent of all thyroid cancers and the follicular type for another 20 percent of cases. These two types of thyroid cancer are the least aggressive and often curable. One risk factor for papillary and follicular thyroid cancer is exposure to radiation, such as nuclear fallout (the Chernobyl incident, for example) or treatments with X-ray or radiation to the head or neck, especially during childhood. (Radioactive iodine exposure and diagnostic X-rays are not considered risk factors.)

Medullary thyroid cancer is often familial (a disease occurring more frequently in a family than would be expected by chance) and typically is more aggressive and not as curable. Anaplastic thyroid cancers are rare and often have a poor prognosis.


Signs/symptoms
The most common symptom of thyroid cancer is a painless lump in the neck. If the lump presses on other structures in the neck, such as the windpipe, vocal cords or esophagus (the tube that connects the throat and stomach), you may also notice the following symptoms:
difficulty swallowing
tight or full feeling in the neck
pain in the neck
hoarseness
difficulty breathing
enlargement of lymph nodes (small, round structures located throughout the body that help protect the body from invasion by bacteria or other organisms) in the front of the neck

Diagnosis
The doctor will ask questions about your medical history and do a physical exam. To help the doctor determine the exact size and location of the lump and whether it's cancerous, one or more of the following tests may be needed.
Positron emission tomography (PET Scan)
Positron emission tomography (PET scan) is a technique used to monitor metabolism and other body processes. With this procedure, contrast dye injected into a vein is detected by special cameras that produce a cross-sectional image of the body region being studied. A PET scan is often used to assess cancerous tumors and the spread of thyroid cancer.

Needle aspiration biopsy
With needle aspiration, the doctor takes a tissue sample through a small, thin hollow needle. Then, the sample is studied under a microscope. An aspiration helps the doctor determine if cancer cells are present, identify their type, and guide treatment choices.

Thyroid scan
For this test, oral radioactive iodine or other scanning agents help create an image of how the thyroid is functioning on a screen or X-ray film. The iodine identifies active thyroid tissue. If a nodule in the thyroid is functioning excessively, a large amount of iodine will be present. It will appear black in the picture. This is called a hot nodule. If the nodule is functioning inadequately or not at all, little iodine will be present. It will appear white in the picture. This is called a cold nodule. Cold nodules are more likely to be cancerous than hot nodules.

Ultrasound
With ultrasound, sound waves are used to create an image of the thyroid gland. This test helps the doctor evaluate the size and number of nodules and whether they are solid or filled with fluid. Ultrasound can also be used to track the progress of thyroid cancer over time or help the doctor with needle placement during a biopsy. Because it uses no radioactive materials, ultrasound is especially useful for women who are pregnant.

MRI and CT scan
Magnetic resonance imaging (MRI) is an imaging technique based on computer analysis of the body's response to a magnetic field. Computed tomography (CT scan) creates a computer-generated, cross-sectional picture of internal body parts. These pictures help the doctor determine the size of the tumor and any spread to the surrounding tissues, lymph nodes or distant organs, such as the bones, lungs or liver.

Blood tests
Various blood tests can help the doctor determine how well the thyroid is functioning. Although people who have thyroid cancer often have normal blood tests, medullary thyroid cancer may cause elevated levels of calcitonin (a hormone produced by the thyroid gland that, in part, helps regulate the level of calcium in the blood).

After the diagnosis
Once thyroid cancer is diagnosed the doctor assigns a stage, which simply indicates how far the cancer has progressed. The stage may depend on your age, the type of cancer, the size of the tumor and whether it has metastasized (formed other tumors in nearby or distant tissues). The type of thyroid cancer and the stage are used to guide treatment choices and help predict treatment outcomes.


Treatment
A team of medical specialists is often involved in treating thyroid cancer, including the primary care doctor, a surgeon, an endocrinologist (a doctor who specializes in treating disorders of the endocrine glands, such as the thyroid) and a nuclear radiologist (a doctor who administers radioactive iodine). The four types of thyroid cancer each have different treatment options, recommended follow-up care and prognoses. Discuss the benefits and risks of the various treatment options with your doctor.
Surgical options
Unless the cancer has spread to other parts of the body, the thyroid tumor is surgically removed. There is sometimes controversy over the surgical options, which include:

total thyroidectomy (removing the entire thyroid gland)
near-total thyroidectomy (removing a large part of the gland)
rarely, a lobectomy (removing just the tumor, some of the thyroid tissue and any cancerous lymph nodes near the thyroid)
Complications of thyroid surgery may include:

temporary or permanent low calcium levels in the blood
impaired breathing from swelling that affects the airway
bleeding
hoarseness caused by damage to the nerves in the throat controlling the larynx (voice box)
After the thyroid is removed, medication will be prescribed to replace the thyroid hormones that are no longer naturally produced. Thyroid function tests may be used as a monitoring tool after surgery to ensure you're taking the right amount of thyroid medication. Unlike other thyroid disease states, thyroid-stimulating hormone (TSH, a hormone the pitutitary gland produces that controls the thyroid) must be suppressed with thyroid cancers. Depending on the treatment received, the doctor may also use a blood test known as serum thyroglobulin to monitor for a recurrence or spread of papillary or follicular thyroid cancer.

Medical options
After surgery, oral radioactive iodine may be used to destroy any remaining cancer cells in the thyroid, surrounding area or other parts of the body. Rarely, an external beam of radiation may be used to destroy a tumor in the thyroid area or distant tissues. Although it's rarely helpful, chemotherapy (cancer-killing medications) may be recommended if the tumor doesn't respond to other treatments.

Treatment outcome
Thyroid cancer treatment is often successful, especially if:

the patient is young
the tumor is less than 1.5 centimeters in diameter
the lymph nodes are free of cancer cells
the cancer has not spread to other parts of the body
the tumor type is nonaggressive (papillary or follicular)
If you have papillary or follicular cancers, you will periodically be taken off your thyroid medication and undergo a radioiodine scan to check for recurrences.

Continuing research on thyroid cancer and its treatment may bring further improvement in survival rates.


Complications
Thyroid cancer may recur or spread to the lymph nodes, lungs or other parts of the body. Careful monitoring and treatment can help prevent complications, however. See your doctor for regular follow-up visits, and notify your doctor of any changes in your health status.

Pregnancy-specific information
Pregnancy is not a risk factor for developing thyroid cancer. Should a thyroid nodule develop during pregnancy, studies indicate that ultrasound and fine needle aspiration biopsy (as described above) are safe during pregnancy. If thyroid cancer is diagnosed during pregnancy, surgery may be done preferably during the second trimester or after delivery. The timing of surgery will depend on the type of cancer and how advanced it is. Make sure you understand all the facts before making a decision about surgery.
Radioactive iodine is not appropriate for diagnosis or treatment during pregnancy because it will destroy the fetus' thyroid.


Senior-specific information
The risk of developing thyroid cancer increases with age.

Prevention
If you have a family history of thyroid cancer or you've received radiation treatments, see your doctor for regular medical exams to check for thyroid abnormalities. If you've inherited a genetic form of medullary thyroid cancer and the diagnosis is confirmed with genetic testing, your doctor may suggest surgical removal of the healthy thyroid gland to prevent cancer from developing.