Thyroid Cancer
Thyroid cancer develops in a small butterfly-shaped gland at the base of your neck that controls vital body functions like heart rate, metabolism, and body temperature. While it is less common than many other cancers, its diagnosis has been rising worldwide, largely due to better detection methods. The good news is that most thyroid cancers are highly treatable, with excellent survival rates when caught early.
Table of contents
- What is thyroid cancer?
- Types of thyroid cancer
- Risk factors and causes
- Signs and symptoms
- How thyroid cancer is diagnosed
- Treatment options
- Outlook and survival
- Living with and after thyroid cancer
What is thyroid cancer?
Thyroid cancer is a disease in which malignant (cancer) cells form in the tissues of the thyroid gland[1]. The thyroid is a small, butterfly-shaped gland located at the base of your neck, just above your windpipe. This gland produces hormones that regulate your body’s metabolism—how your body uses energy. These hormones also help control your body temperature, blood pressure, and heart rate[2].
- Thyroid gland
- Neck
- Trachea (windpipe)
The thyroid uses iodine, a mineral found in some foods and in iodized salt, to help make several hormones. The gland is shaped like a butterfly, with a right lobe and a left lobe. A thin piece of tissue called the isthmus connects the two lobes[6]. A healthy thyroid is a little larger than a quarter and usually cannot be felt through the skin.
Each year, about 44,000 to 53,000 Americans are diagnosed with thyroid cancer[2][5]. While the incidence has been steadily increasing worldwide over the past several decades, the mortality rate has remained stable. This increase is largely due to early detection and advanced imaging technology such as ultrasounds, CT scans, and MRI, which can incidentally detect small thyroid nodules[4].
Types of thyroid cancer
Thyroid cancer can be classified into several main types based on the type of cells from which the cancer grows. The behavior of thyroid cancer varies widely, from slow-growing tumors to highly aggressive forms[4].
Papillary thyroid cancer is the most common type, making up about 70% to 80% of all thyroid cancers[5]. This cancer type grows slowly and can occur at any age. Although papillary thyroid cancer often spreads to lymph nodes in your neck, it responds very well to treatment. It is highly curable and rarely fatal[2].
Follicular thyroid cancer accounts for about 10% to 15% of thyroid cancer diagnoses[2][5]. This cancer is more likely to spread to your bones and organs, like your lungs. When cancer spreads to distant organs, it is called metastatic cancer, which may be more challenging to treat. Most patients with follicular thyroid cancer are over the age of 40[16].
Medullary thyroid cancer accounts for about 2% to 4% of all thyroid cancers[2][7]. This is a neuroendocrine tumor that develops in the C cells of the thyroid. The C cells make a hormone called calcitonin that helps maintain a healthy level of calcium in the blood[6]. About 25% of people with medullary thyroid cancer have a family history of the disease. A faulty gene or genetic mutation may be to blame[2].
Anaplastic thyroid cancer is the rarest form of thyroid cancer, accounting for only 1% to 2% of cases[2][7]. This is the most aggressive type and the hardest to treat. It can grow quickly and often spreads into surrounding tissue and other parts of your body. Most patients with anaplastic thyroid cancer are over the age of 60[16].
Papillary and follicular thyroid cancers are also known as well-differentiated thyroid cancers and account for over 90% of all thyroid cancers[7]. These cancers can be treated and can usually be cured[6].
Risk factors and causes
The exact cause of thyroid cancer is unknown in most cases. When cancer develops in the thyroid, changes occur in the DNA of thyroid cells that cause them to grow and multiply abnormally. Where healthy cells typically die, these abnormal cells grow and eventually form a tumor[1].
Several factors can increase your chances of developing thyroid cancer. Women are three times more likely to develop thyroid cancer compared to men[1][2]. The disease is commonly diagnosed in women in their 40s and 50s and men in their 60s and 70s. However, even children can develop the disease[2].
Exposure to high levels of radiation is one of the primary risk factors for thyroid cancer. This includes radiation therapy to the head or neck for other cancers, which can increase your risk[1]. Before 1960, some people had low-dose radiation targeted at the head and neck to treat non-cancerous conditions. Large-scale radiation exposure has also occurred due to nuclear accidents such as Chernobyl and atomic bombs[22].
Family history plays a role in thyroid cancer risk. A family history of thyroid cancer in a close family member—parent, grandparent, sibling, or child—increases the risk of developing the disease[22]. About 5% of papillary and follicular thyroid cancers and 15% to 30% of medullary thyroid cancers have a familial occurrence[4].
Certain hereditary genetic conditions can also increase risk. Medullary thyroid cancer is sometimes caused by a change in a gene that is passed from parent to child. The most well-known genetic cause is the MEN2 (Multiple Endocrine Neoplasia) syndromes associated with mutations in the RET gene[22]. Papillary thyroid cancer is associated with FAP (Familial Adenomatous Polyposis), while follicular thyroid cancer can be linked to Cowden Syndrome and Carney Complex[22].
It is important to note that thyroid cancer is not associated with lifestyle factors. It has nothing to do with alcohol consumption, cigarette smoking, or diet[18].
Signs and symptoms
Many people with early-stage thyroid cancer do not have obvious symptoms. Most don’t think they have cancer until they go for an annual physical exam, and the doctor suspects a problem after feeling the neck and detecting a lump or swelling[18].
The most common sign of thyroid cancer is a lump or growth in your neck called a thyroid nodule. You or your healthcare provider might feel this lump during a routine medical exam[2]. It is important to note that most thyroid nodules are not cancer—only about 3 out of 20 thyroid nodules turn out to be cancerous[2].
As thyroid cancer develops, other symptoms can include difficulty breathing or swallowing, loss of voice or hoarseness, and swollen lymph nodes in your neck[2]. Some people may experience pain in the throat or neck[7].
If you have thyroid cancer that has spread to other areas of your body, you may experience additional symptoms such as tiredness, loss of appetite, nausea and vomiting, and unexpected weight loss[2].
How thyroid cancer is diagnosed
There is no standard or routine screening for thyroid cancer. Usually, it is detected when a healthcare provider feels abnormal swelling during a physical exam while palpating the neck[18].
When a thyroid nodule is found, several tests are used to diagnose thyroid cancer. An ultrasound of the thyroid is often the first step. This imaging test can show whether the swelling is due to a thyroid nodule and provide information about its characteristics[18].
If a suspicious nodule is identified, a fine-needle aspiration biopsy is often performed. This procedure involves the insertion of a needle into the nodule with ultrasound guidance to remove a small piece of tissue. The tissue is then examined under a microscope to determine whether cancer is present[18].
Blood tests may also be done to check thyroid hormone levels and for antithyroid antibodies in the blood. These tests help check for other types of thyroid disease. For medullary thyroid cancer, blood tests may measure levels of calcitonin, a hormone made by C cells[6].
A comprehensive, high-resolution ultrasound is important because thyroid cancer commonly spreads to lymph nodes in the neck. If these lymph nodes test positive for thyroid cancer, the surgeon will need to remove both the thyroid and the lymph nodes during surgery[10].
Other imaging tests may be ordered, including CT scans, MRI, or PET scans, to help determine the extent of the cancer and whether it has spread to other parts of the body[4].
Treatment options
Most types of thyroid cancer can be treated and cured, especially when the cancer is localized and has not spread to surrounding areas. For people with thyroid cancer, the goal is to remove the cancer by performing surgery and stop it from growing and returning[12].
Surgery
Surgery is the most common treatment for thyroid cancer and is the main treatment for thyroid nodules and tumors, except for some anaplastic thyroid cancers[4]. Doctors may remove part of or the entire thyroid gland. This is called a thyroidectomy.
If nearly all of the thyroid gland is removed, it is known as a near-total thyroidectomy. If the entire thyroid gland is removed, it is called a total thyroidectomy[12]. If only part of the thyroid is removed—typically one lobe—this is called a lobectomy or partial thyroidectomy. This approach is typically used for small differentiated thyroid cancers with no sign of spread[12].
During surgery, nearby lymph nodes and affected tissue may also be removed if the cancer has spread to those areas[12]. The surgeon makes a small incision along the neck, which usually leaves behind a small scar that typically fades with time[12].
Radioactive iodine therapy
Radioactive iodine therapy uses a radioactive form of iodine called iodine 131 (I-131). The thyroid gland absorbs nearly all the iodine in the body. When you take radioactive iodine as a pill or drink, thyroid cells absorb the iodine 131, and the radiation in the iodine kills the cancer cells[17].
This treatment is only suitable for some types of thyroid cancer, including follicular and papillary thyroid cancer. It is not used for medullary thyroid cancer[12]. Radioactive iodine therapy is often used after surgery to destroy any remaining thyroid tissue and cancer cells, or to treat cancer that has come back or spread to another part of the body[15].
Thyroid hormone therapy
If you have had surgery to remove your thyroid, you will need to take daily thyroid hormone pills to replace the hormones your thyroid gland normally made. This is essential for your body to function properly[15].
For most thyroid cancer patients, the dose of thyroid hormone replacement is usually high enough to suppress thyroid-stimulating hormone (TSH) well below the normal range. This helps prevent the growth of any remaining cancer cells while providing essential thyroid hormone to the body[7].
Targeted therapy
Targeted medicines aim to stop cancer growing by attacking specific targets on cancer cells. These drugs, called tyrosine kinase inhibitors, may be used for thyroid cancer if other treatments are not an option or are no longer working, or if the cancer has spread to another part of the body[2][15].
External beam radiation therapy
External beam radiation therapy uses high-energy X-rays or other types of radiation to kill cancer cells or keep them from growing. A machine called a linear accelerator delivers precise beams that target cancer cells while sparing surrounding normal tissue[16].
This treatment may be used for thyroid cancer if the cancer cannot be removed by surgery or has spread to another part of the body[15]. Treatment is typically delivered for short periods of time, five days a week for four to six weeks[16].
Chemotherapy
Chemotherapy uses medicines to kill cancer cells. It is not usually used to treat thyroid cancer, but you may have it if the cancer has come back or has spread to another part of your body. Anaplastic thyroid cancer patients may receive chemotherapy with external beam radiation therapy[6][15].
Outlook and survival
The prognosis for most patients with thyroid cancer is excellent. Thyroid cancer is generally highly treatable, with an excellent cure rate. The overall 5-year survival rate for people with thyroid cancer is 98%[2]. Long-term survival is 95% or higher[7].
Because most thyroid cancers are so slow-growing, doctors use a 10-year survival scale rather than the typical 5-year scale used for most cancers. The average 10-year survival can be well over 90%[18].
Papillary thyroid cancer has a generally excellent outlook, even if there is spread to the lymph nodes. This cancer is highly curable and rarely fatal[5]. Well-differentiated tumors, including papillary and follicular thyroid cancer, can usually be cured[6].
However, thyroid cancer is still serious. Like any cancer, if it is not diagnosed early and successfully treated, it can spread to other organs, cause complications, and possibly even be fatal[18]. Despite the excellent prognosis, approximately 2,000 patients die from thyroid cancer each year in the United States[5].
Poorly differentiated and undifferentiated tumors, such as anaplastic thyroid cancer, are less common but grow and spread quickly and have a poorer chance of recovery[6].
Living with and after thyroid cancer
Life after thyroid cancer looks different for everyone, and survivorship concerns vary from person to person. Many thyroid cancers remain stable, microscopic, and indolent. Early diagnosis and appropriate treatment can improve prognosis and reduce mortality[14].
The rate of recurrence for thyroid cancer can be up to 30%, and recurrences can occur even decades after the initial diagnosis. Therefore, it is important that patients get regular follow-up examinations to detect whether the cancer has re-emerged. Monitoring should continue throughout the patient’s lifetime[7].
Follow-up care typically includes a review of medical history together with selected blood tests appropriate for the type of cancer and stage of treatment. These may include TSH, thyroglobulin, CEA, and calcitonin levels. Physical examination and imaging techniques such as ultrasound, radioiodine whole body scan, chest X-ray, CT, MRI, or PET scans may also be used[7].
If you have had your thyroid removed, you will need to take thyroid hormone replacement medication for life. This medication helps your body perform the functions your thyroid used to carry out. It is also not uncommon to need calcium supplements if parathyroid glands were affected during surgery[24].
Some people experience short-term side effects from treatment, such as pain or discomfort at the incision site, temporary voice changes after surgery, and temporary low blood calcium levels. Long-term, many patients live healthy lives with appropriate medication and follow-up care[24].
Coping with a cancer diagnosis can be difficult emotionally. You may feel angry, sad, or anxious. All sorts of feelings are likely to come and go, which is a natural part of coming to terms with the disease. Talking to your friends and relatives, joining a support group, or contacting thyroid cancer charities can provide valuable support[20].
It is important to ask your healthcare team questions about what to expect from thyroid cancer survivorship. Questions might include what follow-up care you will need, how frequently you should see your cancer care team, what short-term and long-term side effects of treatment you can expect, and what steps you can take to improve your lifestyle and reduce your chance of recurrence[24].
