Thyroid cancer facts
- The thyroid gland produces thyroid hormones which are important in the normal regulation of the metabolism of the body.
- Thyroid cancer is three times more common in women than in men.
- There are four major types of thyroid cancer: papillary, follicular, medullary, and anaplastic.
- The cause of thyroid cancer is unknown, but certain risk factors have been identified and include a family history of goiter, exposure to high levels of radiation, and certain hereditary syndromes.
- The National Cancer Institute recommends that anyone who received radiation to the head or neck in childhood be examined by a doctor every one to two years to detect potential thyroid cancer.
- The most common signs and symptoms of thyroid cancer include a lump, or thyroid nodule, that can be felt in the neck, trouble swallowing, throat or neck pain, swollen lymph nodes in the neck, cough, and vocal changes.
- The only certain way to tell whether a thyroid lump is cancerous is by examining the thyroid tissue obtained using a needle or surgery for biopsy. A CEA blood test, physical exam, X-rays, CT scans, PET scans, ultrasounds, and MRIs may also be used to help establish a definitive diagnosis and determine staging.
- Surgery is the most common form of treatment for thyroid cancer that has not spread to other areas of the body. Radiation therapy, chemotherapy, and radioactive iodine treatment are also treatment options for thyroid cancer.
- The survival rate and prognosis of thyroid cancer depends upon a few factors, including the individual's age, the size of the tumor, and whether the cancer has metastasized.
- It is not possible to prevent most cases of thyroid cancer.
What is the thyroid?
The thyroid gland is located in the front of the neck and is most well-known and responsible for producing thyroid hormone, the chemical in the body that is responsible for regulating the body's metabolism.
Parafollicular cells in the thyroid produce the thyroid hormone. Too much thyroid production can cause hyperthyroidism (hyper=too much) where a person can experience rapid heartbeat and palpitations, sweating, heat intolerance, weight loss, and anxiety. Hypothyroidism (hypo=too little) may cause lethargy, weight gain, hair thinning, gravelly voice, and cold intolerance. The pituitary gland in the brain controls the amount of thyroid hormone that is produced by secreting thyroid stimulating hormone (TSH).
C cells in the thyroid produce a hormone called calcitonin that helps to regulate calcium levels in the body.
Other cells that are found in the thyroid include lymphocytes that are part of the body's immune system and stromal cells that help support the architecture of the thyroid gland itself.
What is the thyroid cancer?
Thyroid cancer affects up to 20, 000 people in the US every year but accounts for only 1% of new cancers that develop in the US.
DNA (mutations) that occur spontaneously or in response to an environmental exposure or toxic substances can alter normal thyroid cells. The genetic changes cause the cells to multiply very rapidly without the normal controls found in the rest of the gland. Any of the cell types found in the thyroid gland can mutate into a specific type of cancer.
Cancer is different than goiter, an enlargement of the thyroid gland that may be associated with hyper or hypothyroidism. Worldwide, the most common cause of goiter is iodine deficiency. In countries where table salt is iodinated, the autoimmune disease Hashimoto's thyroiditis, is the most common cause. Grave's disease, another autoimmune disease, can also be associated with thyroid enlargement.
What causes thyroid cancer?
The exact cause of thyroid cancer is not known, though there are factors that may be associated with an increased risk of developing the cancer. Even if the risk factors are present, there is not a way of knowing whether cancer might develop; patients without risk factors still may develop thyroid cancer.
What are the risk factors for thyroid cancer?
Children who have had radiation exposure to the neck are at higher risk for thyroid cancer. Studies have looked at children who were radiated 50 and 60 years ago when the risks of radiation where less well understood, and their rate of thyroid cancer is increased. Children and women survivors of nuclear reactor accidents (Chernobyl in 1986 has been studied) have an increased risk of thyroid and other types of cancer.
X-rays and CT scans of the neck use low doses of radiation but medical testing has not been found to cause thyroid cancer. Nevertheless, in general, it is important to limit the amount of exposures to the least amount of radiation that will provide a clear enough image to help make a diagnosis.
Diets low in iodine may increase the risk of thyroid cancer, but in developed countries, there is usually enough iodine used as food additives that this is not a problem. Lower levels of iodine in the diet may enhance the risk of radiation induced thyroid cancer.
Women are three times more likely to develop thyroid cancer than men and at a slightly younger age (40 to 50 years old for women versus 60 to 70 for men).
There may be a genetic predisposition to thyroid cancer, especially in certain rare types of thyroid cancer.
What are the symptoms and signs of thyroid cancer?
Most often, a thyroid cancer is found when the patient or the patient's health care professional feels (palpates) a lump or nodule in the lower front of the neck where the thyroid is located. It is most often painless and found incidentally, by chance. Occasionally, an enlarged lymph node may be palpated by itself in the more lateral neck or in addition to a thyroid nodule.
Most patients have normal thyroid function at the time the nodule is discovered and have no symptoms related to hyper or hypothyroidism.
It the tumor grows locally, it may cause difficulty swallowing food (dysphagia) if it compresses the esophagus (which is rare) or hoarseness if the recurrent laryngeal nerve that is located near the thyroid gland -- which controls the vocal cords -- is invaded and causes vocal cord paralysis.
What are thyroid nodules?
A thyroid nodule is an abnormal growth found within the thyroid gland. It may be solid, fluid filled (cystic) -- usually with a jelly like substance called colloid -- or a combination of both.
Most often nodules are found incidentally when the patient or health care professional feels the neck. Whether the nodule is benign or cancerous cannot necessarily be determined just by feeling it and further tests may be warranted.
What are the different types of thyroid cancer?
Thyroid cancers are classified based upon which cell type is involved.
Well differentiated cancers (in which thyroid cells are less abnormal looking) include:
- Papillary thyroid cancer: This is the most common type of thyroid cancer accounting for 80% of cases.
- Hurthle cell carcinoma: This is a rare variant of papillary cancer (also known as oncocytic carcinoma).
- Follicular thyroid cancer: This is the second most common type of thyroid cancer accounding for 10% of cases.
- Medullary thyroid cancer: This thyroid cancer type arises from the C cells in the thyroid and comprises 5% of all cases.
- Anaplastic thyroid cancer: This rare cancer involves thyroid cells are very abnormal looking, accounting for 1% of all cases.
- Lymphoma: This rare cancer is most often non-Hodgkin's B cell type.
- Sarcoma: This type of thyroid cancer is very rare.
How is thyroid cancer diagnosed?
Once a lump in the thyroid is discovered, it is important to know whether it is benign or malignant (cancerous).
Often an ultrasound is performed to assess whether there is a single nodule or multiple nodules are present. Ultrasound can determine whether the nodule is fluid filled or solid. Ultrasound also can determine the general appearance of thyroid looking for inflammation or irregularities and the presence of enlarged lymph nodes nearby that may represent metastatic cancer.
Fine needle aspiration biopsy is the procedure performed to obtain a sample of cells from the nodule to determine if it is cancerous. Using ultrasound, a thin needle is placed into the nodule and cells from the nodule are obtained. These cells can be examined under a microscope by a pathologist to determine whether a cancer is present and if so, what type of cancer it is.
Results of the aspiration are usually reported as the following:
- Malignant: risk of malignancy is 100%
- Suspicious for malignancy: risk of malignancy is 50% to 75%
- Follicular cancer: risk of malignancy is 20% to 30%
- Atypical cells of unknown significance: risk of malignancy is 5% to 10%
- Benign: risk of malignancy is less than 1%
- Sometimes, the results of the aspiration are unclear and indeterminate, and the aspiration may need to be repeated to get a better sample and more cells to study.
Another test involves ingesting radioactive iodine, which is taken up by the thyroid gland. The gland is scanned by a Geiger counter-type of apparatus that determines how much radioactive iodine has been taken up by the gland and any thyroid nodules. If the nodule picks up much of the iodine, it is referred to as a "hot nodule." Such nodules are rarely cancerous. Nodules that take up little to no iodine are referred to as "cold nodules." Although the overwhelming majority of such nodules are benign, 5% turn out to be malignant. Although thyroid scans may be helpful, aspiration of the gland is a much more useful test.
Blood tests may be ordered to determine thyroid hormone levels and levels of other hormones and electrolytes, like calcium, within the body. These tests indicate whether the cells of the thyroid produce too much or too little hormone, not if cancer is present.
On occasion CT, MRI, or PET scans may be useful in evaluating the neck structures if there is concern that thyroid cancer has spread (metastasized).
How is thyroid cancer staging determined?
Thyroid cancer, like most others, is staged based upon three criteria:
- T = how large the main tumor is when it is found
- N = the presence of cancer in lymph nodes and their location
- M = whether the cancer has spread or metastasized to other parts of the body. Thyroid cancer has been known to spread locally or to distant parts of the body including lungs and bone.
Staging from I to IV, including subgroups, is different for each type of cancer and helps predict outcome and survival. There are also different staging considerations for patients older or younger than age 45 for papillary and follicular thyroid cancers.
What kinds of specialists treat thyroid cancer?
A variety of physicians may be involved in the evaluation, diagnosis, and treatment of thyroid cancer. Primary care professionals may help coordinate care and may be the persons who make the initial diagnosis of thyroid gland abnormalities. Endocrinologists are specialists who specifically care for the thyroid. Surgeons may operate on the thyroid gland and thyroid cancer; these may be general surgeons or those with special training in head and neck surgery. Interventional radiologists may help with aspiration to obtain tissue samples, but this is also frequently performed by endocrinologists. Radiation oncologists, who are trained to provide radiation therapy treatments, may occasionally be asked to provide treatment. The care of thyroid cancer requires a team approach, but the members vary depending upon geographic location and availability of specialists.
What is the treatment for thyroid cancer?
Thyroid cancer is treated with a variety of therapies depending on the type and extent of cancer and the health of the patient.
Surgery
Most thyroid cancers require surgery to remove the tumor. Two options are available and decisions as to which option to pursue depend upon the clinical situation.
- Lobectomy: The thyroid has two lobes joined in the middle with a fibrous tissue bridge. If the tumor is confined to only a small area, the surgeon may just remove the affected lobe.
- Thyroidectomy: This is the most common surgery for thyroid cancer and the goal is to completely remove the thyroid gland and hopefully ensure that the cancer will not recur.
- Lymph node resection: Thyroid cancer can spread to local lymph nodes, and these nodes often are removed. Affected lymph nodes may only be recognized at the time of surgery.
- Open biopsy: Sometimes, the cancerous nature of a thyroid nodule is unclear, even after fine needle aspiration. A surgeon may operate to remove the nodule and make the diagnosis of cancer.
Thyroid hormone
Once the thyroid has been removed, the body will no longer be able to make thyroid hormone, and daily thyroid hormone replacement will be necessary. Routine thyroid hormone blood tests will need to be performed to ensure there is an adequate amount of thyroid hormone to allow the body to function properly. Thyroid hormone replacement will be lifelong in total thyroidectomy patients.
Radioactive iodine
Iodine is routinely absorbed by thyroid tissue. Radioactive iodine may be administered after surgery to destroy any remnant thyroid tissue remaining after thyroidectomy. The decision to use this treatment depends upon the type and extent of the thyroid cancer and the levels of thyroid stimulating hormone (TSH) produced by the pituitary gland.
Radiation
In certain thyroid cancers, where the tumor does not take up iodine, radiation therapy may be considered in place of radioactive iodine. Radioactive iodine update tests performed before surgery can assess whether or not iodine is taken up by the thyroid gland.
Chemotherapy
Chemotherapy is not commonly used for most thyroid cancers but may be used in certain clinical situations when the thyroid cancer does not respond to other treatments.
What kind of support is available for those with thyroid cancer?
Patients, families, and friends are all affected when the diagnosis of cancer is made. Support is available not only for the patient but for all those who are close to the patient. Hospitals, clinics, and health care professionals' offices often have specially trained staff to help patients and families address their physical, emotional, and spiritual needs.
It is important for the patient and family to understand the disease, the treatment options, the expected outcomes, and the journey that will occur with cancer. It is important for all involved to advocate for the patient since there is so much information to understand and absorb; it can be overwhelming.
There are many community resources available as well. The American Cancer Society is a good place to begin. They have local offices and may be contacted online.
What is the prognosis for patients with thyroid cancer?
There are many types of thyroid cancer, and outcome depends upon the type of thyroid cancer and its stage.
Patients who have papillary or follicular cancer that is confined to the thyroid gland may expect a normal life expectancy with treatment. Prognosis may be better for women who are younger than 40 years of age.
Patients with anaplastic cancer do poorly, with many surviving only a few months after diagnosis. The 5-year survival rate for this cancer is less than 10%.
Can thyroid cancer be prevented?
There is little one can do to prevent thyroid cancer aside from avoiding excessive exposure to radiation.