Thyroid Cancer
Introduction:
This page is about cancer* that begins in the thyroid. Each year in the United States, more than 25,000 women and 8,000 men learn they have thyroid cancer.
The Thyroid
Your thyroid is a gland at the front of your neck beneath your voice box (larynx). A healthy thyroid is a little larger than a quarter. It usually cannot be felt through the skin.
The thyroid has two parts (lobes). A thin piece of tissue (the isthmus) separates the lobes.
The thyroid makes hormones:
- Thyroid hormone: Thyroid hormone is made by thyroid follicular cells. It affects heart rate, blood pressure, body temperature, and weight.
- Calcitonin: Calcitonin is made by C cells in the thyroid. It plays a small role in keeping a healthy level of calcium in the body.
Four or more tiny parathyroid glands are behind the thyroid. They are on its surface. They make parathyroid hormone, which plays a big role in helping the body maintain a healthy level of calcium.
The pictures show the front and back of the thyroid.
Cancer Cells
Cancer begins in cells, the building blocks that make up tissues. Tissues make up the organs of the body.
Normal, healthy cells grow and divide to form new cells as the body needs them. When normal cells grow old or get damaged, they die, and new cells take their place.
Sometimes, this orderly process goes wrong. New cells form when the body does not need them, and old or damaged cells do not die as they should. The build-up of extra cells often forms a mass of tissue called a growth or tumor.
Growths on the thyroid are often called nodules. Most thyroid nodules (more than 90 percent) are benign (not cancer). Benign nodules are not as harmful as malignant nodules (cancer):
- Benign nodules
- are rarely a threat to life
- don't invade the tissues around them
- don't spread to other parts of the body
- usually don't need to be removed
- Malignant nodules
- may sometimes be a threat to life
- can invade nearby tissues and organs
- can spread to other parts of the body
- often can be removed or destroyed, but sometimes the cancer returns
Cancer cells can spread by breaking away from the original tumor. They enter blood vessels or lymph vessels, which branch into all the tissues of the body. The cancer cells attach to other organs and grow to form new tumors that may damage those organs. The spread of cancer is called metastasis.
Types of Thyroid Cancer
There are several types of thyroid cancer:
- Papillary thyroid cancer: In the United States, this type makes up about 80 percent of all thyroid cancers. It begins in follicular cells and grows slowly. If diagnosed early, most people with papillary thyroid cancer can be cured.
- Follicular thyroid cancer: This type makes up about 15 percent of all thyroid cancers. It begins in follicular cells and grows slowly. If diagnosed early, most people with follicular thyroid cancer can be treated successfully.
- Medullary thyroid cancer: This type makes up about 3 percent of all thyroid cancers. It begins in the C cells of the thyroid. Cancer that starts in the C cells can make abnormally high levels of calcitonin. Medullary thyroid cancer tends to grow slowly. It can be easier to control if it's found and treated before it spreads to other parts of the body.
- Anaplastic thyroid cancer: This type makes up about 2 percent of all thyroid cancers. It begins in the follicular cells of the thyroid. The cancer cells tend to grow and spread very quickly. Anaplastic thyroid cancer is very hard to control.
Risk Factors
Doctors often cannot explain why one person develops thyroid cancer and another does not. However, it is clear that no one can catch thyroid cancer from another person.
Research has shown that people with certain risk factors are more likely than others to develop thyroid cancer. A risk factor is something that may increase the chance of developing a disease.
Studies have found the following risk factors for thyroid cancer:
- Radiation: People exposed to high levels of radiation are much more likely than others to develop papillary or follicular thyroid cancer. One important source of radiation exposure is treatment with x-rays. Between the 1920s and the 1950s, doctors used high-dose x-rays to treat children who had enlarged tonsils, acne, and other problems affecting the head and neck. Later, scientists found that some people who had received this kind of treatment developed thyroid cancer.
(Routine diagnostic x-rays - such as dental x-rays or chest x-rays - use very low doses of radiation. Their benefits usually outweigh their risks. However, repeated exposure could be harmful, so it's a good idea to talk with your dentist and doctor about the need for each x-ray and to ask about the use of shields to protect other parts of the body.)
Another source of radiation is radioactive fallout. This includes fallout from atomic weapons testing (such as the testing in the United States and elsewhere in the world, mainly in the 1950s and 1960s), nuclear power plant accidents (such as the Chornobyl [also called Chernobyl] accident in 1986), and releases from atomic weapons production plants (such as the Hanford facility in Washington state in the late 1940s). Such radioactive fallout contains radioactive iodine (I-131) and other radioactive elements. People who were exposed to one or more sources of I-131, especially if they were children at the time of their exposure, may have an increased risk of thyroid diseases. For example, children exposed to radioactive iodine from the Chornobyl accident have an increased risk of thyroid cancer.
- Family history of medullary thyroid cancer: Medullary thyroid cancer sometimes runs in families. A change in a gene called RET can be passed from parent to child. Nearly everyone with the changed RET gene develops medullary thyroid cancer. The disease occurs alone as familial medullary thyroid cancer or with other cancers as multiple endocrine neoplasia (MEN) syndrome.
A blood test can detect the changed RET gene. If it's found in a person with medullary thyroid cancer, the doctor may suggest that family members be tested. For those who have the changed gene, the doctor may recommend frequent lab tests or surgery to remove the thyroid before cancer develops.
- Family history of goiters or colon growths: A small number of people with a family history of having goiters (swollen thyroids) with multiple thyroid nodules are at risk for developing papillary thyroid cancer. Also, a small number of people with a family history of having multiple growths on the inside of the colon or rectum (familial polyposis) are at risk for developing papillary thyroid cancer.
- Personal history: People with a goiter or benign thyroid nodules have an increased risk of thyroid cancer.
- Being female: In the United States, women are almost three times more likely than men to develop thyroid cancer.
- Age over 45: Most people with thyroid cancer are more than 45 years old. Most people with anaplastic thyroid cancer are more than 60 years old.
- Iodine: Iodine is a substance found in shellfish and iodized salt. Scientists are studying iodine as a possible risk factor for thyroid cancer. Too little iodine in the diet may increase the risk of follicular thyroid cancer. However, other studies show that too much iodine in the diet may increase the risk of papillary thyroid cancer. More studies are needed to know whether iodine is a risk factor.
Having one or more risk factors does not mean that a person will get thyroid cancer. Most people who have risk factors never develop cance
Symptoms
Early thyroid cancer often does not have symptoms. But as the cancer grows, symptoms may include:
- A lump in the front of the neck
- Hoarseness or voice changes
- Swollen lymph nodes in the neck
- Trouble swallowing or breathing
- Pain in the throat or neck that does not go away
Most often, these symptoms are not due to cancer. An infection, a benign goiter, or another health problem is usually the cause of these symptoms. Anyone with symptoms that do not go away in a couple of weeks should see a doctor to be diagnosed and treated as early as possible.
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