Thyroid cancer forms in the thyroid gland (an organ at the base of the throat that makes hormones that help control heart rate, blood pressure, body temperature, and weight). Four main types of thyroid cancer are papillary, follicular, medullary, and anaplastic thyroid cancer. The four types are based on how the cancer cells look under a microscope.
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.
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:
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.