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.
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):
- 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
- 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.
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 cancer.
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.
If you have symptoms that suggest thyroid cancer, your doctor will help you find out whether they are from cancer or some other cause. Your doctor will ask you about your personal and family medical history. You may have one or more of the following tests:
- Physical exam: Your doctor feels your thyroid for lumps (nodules). Your doctor also checks your neck and nearby lymph nodes for growths or swelling.
- Blood tests: Your doctor may check for abnormal levels of thyroid-stimulating hormone (TSH) in the blood. Too much or too little TSH means the thyroid is not working well. If your doctor thinks you may have medullary thyroid cancer, you may be checked for a high level of calcitonin and have other blood tests.
- Ultrasound: An ultrasound device uses sound waves that people cannot hear. The device aims sound waves at the thyroid, and a computer creates a picture of the waves that bounce off the thyroid.
The picture can show thyroid nodules that are too small to be felt. The doctor uses the picture to learn the size and shape of each nodule and whether the nodules are solid or filled with fluid. Nodules that are filled with fluid are usually not cancer. Nodules that are solid may be cancer.
- Thyroid scan: Your doctor may order a scan of your thyroid. You swallow a small amount of a radioactive substance, and it travels through the bloodstream. Thyroid cells that absorb the radioactive substance can be seen on a scan. Nodules that take up more of the substance than the thyroid tissue around them are called "hot" nodules.
Hot nodules are usually not cancer. Nodules that take up less substance than the thyroid tissue around them are called "cold" nodules. Cold nodules may be cancer.
- Biopsy: A biopsy is the only sure way to diagnose thyroid cancer. A pathologist checks a sample of tissue for cancer cells with a microscope.
Your doctor may take tissue for a biopsy in one of two ways:
- Fine-needle aspiration: Most people have this type of biopsy. Your doctor removes a sample of tissue from a thyroid nodule with a thin needle. An ultrasound device can help your doctor see where to place the needle.
- Surgical biopsy: If a diagnosis cannot be made from fine-needle aspiration, a surgeon removes the whole nodule during an operation. If the doctor suspects follicular thyroid cancer, surgical biopsy may be needed for diagnosis.
- Thyroid Hormone Treatmen
- Radioactive Iodine Therapy
- External Radiation Therapy
People with thyroid cancer have many treatment options. Treatment usually begins within a few weeks after the diagnosis, but you will have time to talk with your doctor about treatment choices and get a second opinion.
The choice of treatment depends on:
- the type of thyroid cancer (papillary, follicular, medullary, or anaplastic)
- the size of the nodule
- your age
- whether the cancer has spread
You and your doctor can work together to develop a treatment plan that meets your needs.
Your doctor may refer you to a specialist who has experience treating thyroid cancer, or you may ask for a referral. An endocrinologist is a doctor who specializes in treating people who have hormone disorders. You may see a thyroidologist, an endocrinologist who specializes in treating diseases of the thyroid.
You may have a team of specialists. Other specialists who treat thyroid cancer include surgeons, medical oncologists, and radiation oncologists . Your health care team may also include an oncology nurse and a registered dietitian.
Your doctor can describe your treatment choices and the expected results. Thyroid cancer may be treated with surgery, thyroid hormone treatment, radioactive iodine therapy, external radiation therapy, or chemotherapy.
Most patients receive a combination of treatments. For example, the standard treatment for papillary cancer is surgery, thyroid hormone treatment, and radioactive iodine therapy. Although external radiation therapy and chemotherapy are not often used, when they are, the treatments may be combined.
Surgery and external radiation therapy are local therapies. They remove or destroy cancer in the thyroid. When thyroid cancer has spread to other parts of the body, local therapy may be used to control the disease in those specific areas.
Thyroid hormone treatment, radioactive iodine therapy, and chemotherapy are systemic therapies. Systemic therapies enter the bloodstream and destroy or control cancer throughout the body.
You may want to know about side effects and how treatment may change your normal activities. Because cancer treatments often damage healthy cells and tissues, side effects are common. Side effects depend mainly on the type and extent of the treatment.
Side effects may not be the same for each person, and they may change from one treatment session to the next. Before treatment starts, ask your health care team to explain possible side effects and suggest ways to help you manage them.
At any stage of disease, care is available to relieve the side effects of treatment, to control pain and other symptoms, and to help you cope with the feelings that a diagnosis of cancer can bring.
Most people with thyroid cancer have surgery. The surgeon removes all or part of the thyroid. The type of surgery depends on the type and stage of thyroid cancer, the size of the nodule, and your age.
- Total thyroidectomy: This surgery can be used for all types of thyroid cancer. The surgeon removes all of the thyroid through an incision in the neck. If the surgeon is not able to remove all of the thyroid tissue, it can be destroyed by radioactive iodine therapy later.
Nearby lymph nodes also may be removed. If cancer has invaded tissue within the neck, the surgeon may remove nearby tissue. If cancer has spread outside the neck, surgery, radioactive iodine therapy, or external radiation therapy may be used to treat those areas.
- Lobectomy: Some people with follicular or papillary thyroid cancer may have only part of the thyroid removed. The surgeon removes one lobe and the isthmus. Some people who have a lobectomy later have a second surgery to remove the rest of the thyroid. Less often, the remaining thyroid tissue is destroyed by radioactive iodine therapy.
The time it takes to heal after surgery is different for each person. You may be uncomfortable for the first few days. Medicine can help control your pain. Before surgery, you should discuss the plan for pain relief with your doctor or nurse. After surgery, your doctor can adjust the plan if you need more pain relief.
Surgery for thyroid cancer removes the cells that make thyroid hormone. After surgery, nearly all people need to take pills to replace the natural thyroid hormone. You will need thyroid hormone pills for the rest of your life.
If the surgeon removes the parathyroid glands, you may need to take calcium and vitamin D pills for the rest of your life.
In a few people, surgery may damage certain nerves or muscles. If this happens, a person may have voice problems or one shoulder may be lower than the other.
Thyroid Hormone Treatment
After surgery to remove part or all of the thyroid, nearly everyone needs to take pills to replace the natural thyroid hormone. However, thyroid hormone pills are also used as part of the treatment for papillary or follicular thyroid cancer. Thyroid hormone slows the growth of thyroid cancer cells left in the body after surgery.
Thyroid hormone pills seldom cause side effects. Your doctor gives you blood tests to make sure you're getting the right dose of thyroid hormone. Too much thyroid hormone may cause you to lose weight and feel hot and sweaty.
It may also cause a fast heart rate, chest pain, cramps, and diarrhea. Too little thyroid hormone may cause you to gain weight, feel cold and tired, and have dry skin and hair. If you have side effects, your doctor can adjust your dose of thyroid hormone.
Radioactive Iodine Therapy
Radioactive iodine (I-131) therapy is a treatment for papillary or follicular thyroid cancer. It kills thyroid cancer cells and normal thyroid cells that remain in the body after surgery.
People with medullary thyroid cancer or anaplastic thyroid cancer usually do not receive I-131 therapy. These types of thyroid cancer rarely respond to I-131 therapy.
Even people who are allergic to iodine can take I-131 therapy safely. The therapy is given as a liquid or capsule that you swallow. I-131 goes into the bloodstream and travels to thyroid cancer cells throughout the body. When thyroid cancer cells take in enough I-131, they die.
Many people get I-131 therapy in a clinic or in the outpatient area of a hospital and can go home afterward. Some people have to stay in the hospital for one day or longer. Ask your health care team to explain how to protect family members and coworkers from being exposed to the radiation.
Most radiation from I-131 is gone in about one week. Within three weeks, only traces of I-131 remain in the body.
During treatment, you can help protect your bladder and other healthy tissues by drinking a lot of fluids. Drinking fluids helps I-131 pass out of the body faster.
Some people have mild nausea the first day of I-131 therapy. A few people have swelling and pain in the neck where thyroid cells remain. If thyroid cancer cells have spread outside the neck, those areas may be painful too.
You may have a dry mouth or lose your sense of taste or smell for a short time after I-131 therapy. Chewing sugar-free gum or sucking on sugar-free hard candy may help.
A rare side effect in men who receive a high dose of I-131 is loss of fertility. In women, I-131 may not cause loss of fertility, but some doctors advise women to avoid getting pregnant for one year after a high dose of I-131.
Researchers have reported that a very small number of patients may develop a second cancer years after treatment with a high dose of I-131. See the "Follow-up Care" section for information about checkups after treatment.
A high dose of I-131 also kills normal thyroid cells, which make thyroid hormone. After radioactive iodine therapy, you need to take thyroid hormone pills to replace the natural hormone.
External Radiation Therapy
External radiation therapy (also called radiotherapy) is a treatment for any type of thyroid cancer that can't be treated with surgery or I-131 therapy. It's also used for cancer that returns after treatment or to treat bone pain from cancer that has spread.
External radiation therapy uses high-energy rays to kill cancer cells. A large machine directs radiation at the neck or other tissues where cancer has spread.
Most patients go to the hospital or clinic for their treatment, usually 5 days a week for several weeks. Each treatment takes only a few minutes.
The side effects depend mainly on how much radiation is given and which part of your body is treated. Radiation to the neck may cause a dry, sore mouth and throat, hoarseness, or trouble swallowing. Your skin in the treated area may become red, dry, and tender.
You are likely to become tired during radiation therapy, especially in the later weeks of treatment. Resting is important, but doctors usually advise patients to try to stay as active as they can.
Although the side effects of radiation therapy can be distressing, your doctor can usually treat or control them. The side effects usually go away after treatment ends.
Chemotherapy is a treatment for anaplastic thyroid cancer. It's sometimes used to relieve symptoms of medullary thyroid cancer or other thyroid cancers.
Chemotherapy uses drugs to kill cancer cells. The drugs are usually given by injection into a vein. They enter the bloodstream and can affect cancer cells all over the body.
You may have treatment in a clinic, at the doctor's office, or at home. Some people may need to stay in the hospital during treatment.
The side effects of chemotherapy depend mainly on which drugs and how much are given. The drugs can harm normal cells that divide rapidly, such as the cells in the mouth. The most common side effects include nausea, vomiting, mouth sores, loss of appetite, and hair loss.
Your health care team can suggest ways to control many of these side effects. Most side effects go away after treatment ends.
Last Editorial Review: 25/1/2010