Thyroid cancer begins in the thyroid gland. The thyroid gland, also called the thyroid, is located at the front of the neck just below the larynx. It is slightly larger than a quarter and shaped like a butterfly, with a right lobe and a left lobe. The thyroid gland contains mainly two types of cells -- thyroid follicular cells and C cells.
Thyroid cancer begins when the cells in the thyroid gland begin to change and grow uncontrollably, until they form a nodule, also called a thyroid tumor. There are two types of thyroid nodules: benign (noncancerous) and malignant (cancerous). Ninety percent of all thyroid nodules are benign.
RISK FACTORS
Following factors can increase your risk of developing thyroid cancer:
Radiation Exposure
Exposure to high levels of radiation may increase the risk of papillary and follicular thyroid cancers.
Family History of Medullary Thyroid Cancer
Medullary thyroid cancer (MTC) sometimes runs in families. A change in a gene called RET may increase risk for MTC. This altered gene may be passed from parent to child. Nearly everyone with the altered RET gene develops MTC. The altered gene can be detected with a blood test. The disease occurs either alone as familial medullary thyroid cancer or with other cancers as multiple endocrine neoplasia (MEN) syndrome.
Family History of Goiters
A goiter is swelling or lump in the neck due to an enlarged thyroid gland. A goiter is not cancerous. A small number of people with a family history of having goiters are at risk for developing papillary thyroid cancer.
Family History of Colon Growths
A small number of people with a family history of having multiple growths on the inside of the colon are at risk for developing papillary thyroid cancer.
Being Female
Although it is unclear why, thyroid cancer occurs about three times more often in women than in men.
Diet Low in Iodine
Follicular thyroid cancers are more common in areas of the world where people's diets are low in iodine. A diet low in iodine may be more likely to increase the risk of papillary cancer if the person also is exposed to radioactivity. This risk factor does not play a significant role in the US, where iodine is plentiful.
Symptoms
The first symptom of thyroid cancer is usually swelling or a small lump on the front of the neck. This is called a thyroid nodule. Thyroid nodules are common. In more than 90 percent of patients, they are benign (noncancerous).
Other symptoms of thyroid cancer may include:
- Hoarseness
- Trouble swallowing
- Swollen glands in the neck
- Difficulty breathing
- Pain in the throat or neck that does not go away
- A cough that does not go away and is not due to a cold
Most people with thyroid cancer do not show any of these symptoms. Or these symptoms may be similar to those of other medical conditions. If you are concerned about a symptom on this list, please talk with your doctor.
DIAGNOSIS
To diagnose thyroid cancer, your doctor will first ask you about your personal and family medical history. He or she may also use one or more of the following tests:
Physical Examination
The first test for thyroid cancer is a physical examination. Your doctor will feel your thyroid, your throat, and your lymph nodes in the neck for unusual growths or swelling. An unusual growth or swelling may mean a thyroid nodule is present.
Blood Test
Your doctor may use a blood test to check levels of thyroid-stimulating hormone (TSH). An abnormal level may suggest the thyroid is not functioning properly. If your doctor thinks you may have medullary thyroid cancer (MTC), you may be tested for a high level of calcitonin and have other blood tests.
Ultrasound
Ultrasound uses powerful sound waves to detect abnormal growths in the neck. Ultrasound can detect a growth or nodule, but cannot show whether it is malignant (cancerous) or benign. Ultrasound may be used to monitor the size of the nodule.
Radioactive Iodine Scan
A radioactive iodine scan, also called an RAI scan, is used to learn more about a thyroid nodule or to find areas in the body where thyroid cancer cells may be growing quickly. For this test, your doctor will ask you to swallow a small, harmless amount of radioactive iodine. The iodine is absorbed by the thyroid gland (or thyroid cells anywhere in the body), and a special camera is used several hours later to see where the radioactivity has gone.
Biopsy
If you have a thyroid nodule, your doctor may order a biopsy. A biopsy is a procedure in which a small amount of tissue is removed. A pathologist, a doctor who specializes in laboratory tests, will examine the tissue to determine whether it is benign or malignant.
Positron Emission Tomography (PET)
PET is a procedure used to find malignant tumor cells in the body. A small amount of radioactive sugar is injected into a vein. Cancer cells absorb sugar more quickly than normal cells, so they light up on the PET scan. This allows your doctor to see if your cancer has gotten worse or has spread to other parts of the body.
Genetic Screening
An abnormal
RET gene may cause medullary thyroid cancer (MTC). This gene can be passed from parent to child. Not everyone with an altered
RET gene will develop MTC.
Blood tests and genetic tests can detect the
RET gene. People with MTC are encouraged to have genetic testing to determine if a mutation of the
RET gene is present. If you test positive for the
RET gene, your doctor may recommend genetic testing for siblings and children. A genetic counselor can help determine what a positive or negative test result may mean for you and your family.
There are some rare genetic diseases, such as Cowden disease and familial adenomatous polyposis (FAP), that confer an increased risk of thyroid cancer, meaning individuals with those diseases have a higher than average risk of also developing thyroid cancer.
TREATMENT
People with thyroid cancer have many treatment options. Treatment usually begins within a few weeks after the diagnosis. You and your doctor can work together to develop a treatment plan that is right for you.
The type of treatment you will receive is based on several factors. These include:
- Type of thyroid cancer (papillary, follicular, medullary, or anaplastic)
- Size of the nodule
- Your age
- Whether the cancer has spread to other parts of the body
Most people with thyroid cancer receive a combination of treatments. These treatments include:
Surgery
Surgery is the main type of treatment for thyroid cancer. Most patients can be successfully treated with surgery and no further curative treatment is necessary.
The extent of surgery depends on the "risk group" in which you are classified. Low- risk group patients are usually young (ages 20 to50) and have a favorable, small thyroid cancer that is confined to the thyroid gland. The majority of young patients have low-risk thyroid cancer. High-risk group patients are older individuals (older than 50) who have an extensive or aggressive thyroid cancer, which may have spread beyond the thyroid gland. The extent of surgery depends on your risk group stratification.
Your surgeon will most likely perform a procedure called thyroidectomy. This may be a lobectomy, which removes one half of the thyroid gland, or a total thyroidectomy, which removes the entire thyroid.
If your cancer has spread or is at risk of spreading to the lymph nodes, your surgeon may perform a lymphadenectomy. A lymphadenectomy is a surgery to remove the lymph nodes in the neck. A lymphadenectomy is also called a neck dissection or a lymph node dissection.
In cases where all the cancer cells are not able to be surgically removed, surgery may be followed by radioactive iodine therapy or external radiation.
Hormone Treatment
Without the thyroid gland, the body stops producing thyroid hormone, which is essential for proper metabolism and functioning. If you have surgery to remove your thyroid, you will need to begin thyroid hormone therapy.
Thyroid hormone therapy replaces the hormones that the thyroid gland usually produces. Thyroid hormone is also used to decrease the pituitary gland's production of thyroid-stimulating hormone (TSH). Because TSH could potentially cause any remaining cancer cells to grow, sufficient thyroid hormone is given to reduce TSH to desired levels.
Radioactive Iodine Therapy
Some patients may need radioactive iodine treatment after surgery. Patients with medullary thyroid cancer or anaplastic thyroid cancer are not treated with radioactive iodine.
Radioactive iodine is given in either liquid or pill form. Radioactive iodine is given to destroy any normal thyroid tissue. This allows your physicians to maintain your surveillance with blood tests to check a blood marker called thyroglobulin. As the radioactive iodine travels through the body, it is able to find and destroy any thyroid cells that were not removed by surgery or those thyroid cancer cells that have spread beyond the thyroid. Usually only one or two treatments with radioactive iodine are necessary.
In preparation for radioactive iodine treatment, most patients must stop taking thyroid replacement pills for an appropriate period of time before beginning radioactive iodine treatment to help their bodies produce more natural TSH. This approach causes cancer cells to "wake up," making them soak up more radioactive iodine.
Many patients may receive synthetic, or "man-made," human TSH before radioactive iodine therapy to increase TSH levels. This allows patients to continue taking their thyroid pills, which will help them to feel more energetic and alert.
