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The thyroid has two halves, or lobes, one on each side of the neck. It wraps around the trachea (windpipe) just under the larynx (Adam's apple). A thin strip of tissue known as the isthmus connects the two halves.
The thyroid is part of the body's endocrine system, a system of glands that controls hormones in the body. It normally weighs less than an ounce and cannot be seen or felt in most people. However, it has an important function. The thyroid makes hormones that help regulate the body's heart rate, blood pressure, temperature and metabolism (the breakdown of food to create energy).
Thyroid cancer rarely impacts the thyroid gland’s ability to produce hormones. There is no connection between thyroid cancer and common thyroid conditions like hyperthyroidism.
Differentiated thyroid cancer
Most thyroid cancers can be categorized based on how their cells look compared to normal cells. These are called differentiated thyroid cancers. They can be either well differentiated or poorly differentiated.
Cancer cells that look most like normal, healthy cells are well differentiated. Patients with well-differentiated thyroid cancers are most likely to be disease-free at the end of treatment.
Doctors believe most thyroid cancers start as well differentiated. As the cancer grows, its cells can develop additional mutations, changing it to a poorly differentiated cancer. Compared to well-differentiated thyroid cancer, these diseases are harder to treat. They also have a have a higher risk of spreading to the lungs and bones and are more likely to recur after treatment.
Differentiated thyroid cancers develop from follicular cells. Follicular cells produce thyroid hormone, which is important for growth, mental function and metabolism.
Differentiated thyroid cancer types include:
Papillary thyroid cancer: This is the most common type of thyroid cancer. It accounts for about 80% of diagnoses. It occurs in only one lobe of the thyroid gland in 80-90% of cases and both lobes in 10%-20%. Treatment is successful in most cases.
Follicular thyroid cancer: This accounts for less than 10% of thyroid cancers. Though it can be more aggressive than papillary thyroid cancer, follicular thyroid cancer usually grows slowly. Treatment for follicular thyroid cancer is similar to papillary thyroid cancer and is successful for most patients.
Both papillary and follicular thyroid cancer are considered well differentiated cancers. Well-differentiated thyroid cancer tends to stay contained within the thyroid gland. When it does spread outside the thyroid, the most common locations of spread, or metastasis, are lymph nodes, lungs, bones and the liver.
Oncocytic thyroid cancer/Hürthle cell thyroid cancer: Also called oxyphilic cell carcinoma, this disease was considered a type of follicular thyroid cancer until recently. Most patients diagnosed with Hürthle cell carcinoma do well, but the outlook may change based on the extent of disease at the time of diagnosis.
Poorly differentiated thyroid cancer: This is a rare type of thyroid cancer, accounting for less than 5% of all cases.
Anaplastic thyroid cancer
This disease makes up just 1% of thyroid cancer cases. Sometimes called undifferentiated thyroid cancer, it is the rarest and most dangerous type of thyroid cancer. These tumors start as papillary, follicular or Hurtle cell thyroid cancers. They then develop more mutations that cause them to behave very aggressively.
Anaplastic thyroid cancer grows and spreads very rapidly. As it grows, it can move into the trachea and cause breathing problems. Patients with anaplastic thyroid cancer need to seek out treatment immediately.
Some patients are now effectively treated with targeted therapy, surgery, and a combination of chemotherapy and radiation therapy. MD Anderson’s Anaplastic Thyroid Cancer Clinic provides the immediate, specialized treatments these patients require.
Medullary thyroid cancer
Medullary thyroid cancer (MTC) is the only type of thyroid cancer that develops from the parafollicular cells of the thyroid gland.
Parafollicular cells, also known as C cells, produce calcitonin, which helps control calcium metabolism. Most parafollicular cells are in the upper third of each lobe of the thyroid. MTC accounts for less than 5% of thyroid cancers. MTC cells usually produce calcitonin and/or carcinoembryonic antigen (CEA). These proteins can be measured in the blood and used to monitor how the disease is responding to treatment.
Sometimes MTC spreads to the lymph nodes, lungs or liver before a thyroid nodule is found or symptoms develop. MTC can be treated most successfully if it is diagnosed before it has spread.
There are two types of MTC:
- Sporadic MTC accounts for 85% of medullary thyroid cancers. It occurs mostly in older adults and is not inherited.
- Familial MTC is inherited. It often seen in childhood or early adulthood. If familial MTC occurs in association with tumors of certain other endocrine organs (such as the parathyroid and adrenal glands), it is called multiple endocrine neoplasia type 2 (MEN 2). Patients with MTC should undergo genetic testing to learn if they have inherited the gene that causes familial MTC. If they have the gene, their parents, siblings and children should also get genetic testing.
Thyroid cancer statistics
About 44,000 people are diagnosed with thyroid cancer each year in the United States. More than half of the cases occur between ages 20 and 55. The disease is slow growing and responds well to treatment. Its five-year survival rate is more than 98%.
Thyroid cancer risk factors
A risk factor is anything that increases a person’s chance of developing a specific disease.
Less than 1% of thyroid cancers are tied to a risk factor other than age and gender. Certain risk factors have been identified, though. They include:
- Exposure to high levels of radiation, especially during childhood: Radiation exposure is the most significant risk factor for thyroid cancer. This exposure typically comes in the form of radiation treatment to the head and neck area for a childhood cancer. Occasional X-rays or scans that are part of routine medical procedures (such as a dental exam) have very low levels of radiation and are not risk factors.
- Inherited disorders: Familial medullary thyroid cancer is usually caused by an inherited mutation in the RET gene. People who inherit the gene are likely to develop medullary thyroid cancer. Other types of thyroid cancer also may be caused by diseases that run in families. People with a history of thyroid cancer in their family should consider genetic counseling to learn and manage their risk.
- Iodine deficiency: The thyroid uses iodine to make hormones. People with low iodine levels have a higher risk of developing thyroid cancer. This risk factor is uncommon in the United States, where iodine often is added to table salt.
- Age: Over half of thyroid cancer cases occur between ages 20 and 55.
- Gender: Women are three times as likely as men to develop thyroid cancer. Papillary thyroid cancer, the most common type of the disease, is found most often in women of childbearing age.
Not everyone with risk factors gets thyroid cancer. However, if you have risk factors it is a good idea to discuss them with your doctor.
Some cases of thyroid cancer can be passed down from one generation to the next. Genetic counseling may be right for you. Learn more about the risk to you and your family on our genetic testing page.
Why choose MD Anderson for thyroid cancer treatment?
Where you go first for cancer care matters. For thyroid cancer, getting the best treatment the first time is important, since the disease is much more difficult to treat if it returns.
MD Anderson’s Endocrine Center sees more thyroid cancer patients than almost every hospital in the country. This gives its doctors and surgeons incredible expertise when developing your treatment plan. You will receive customized care for thyroid cancer from a team of renowned experts who work together to coordinate your care.
Your personal medical team will be made up of experts from several specialties. They work together, communicating and collaborating with each other and with you, to ensure you receive seamless, coordinated care.
If your treatment for thyroid cancer includes surgery, our surgeons use the most advanced techniques that are proven to have good results. These surgeons are skilled in performing complex surgeries, including procedures for residual cancers, recurrent cancers and cancers that impact critical structures in the head and neck area.
The Endocrine Center also specializes in treating patients with rare and aggressive thyroid cancers. The first drug to get FDA approval for anaplastic thyroid cancer treatment was developed through MD Anderson research. Today, we offer these patients rapid, specialized care in our Anaplastic Thyroid Cancer Clinic.
We remain at the forefront of research on preventing and treating thyroid cancer. We are constantly researching new therapies, new drugs and new drug combinations designed to cure thyroid cancer, extend life and improve patients’ quality of life.
Through this work, we are able to offer clinical trials for innovative treatments. These include studying the use of therapies to shrink tumors before surgery and the expanded use of targeted therapy for some patients.
And at MD Anderson you will also be surrounded by the strength of one of the world’s largest and most experienced cancer centers. From support groups to counseling to integrative medicine care, we have all the services needed to treat not just the disease, but the whole person.
Every day is a new day to live. I choose to live an incredible life no matter my diagnosis.
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Prevention & Screening
Many cancers can be prevented with lifestyle changes and regular screening.