medical information

Thyroid cancer | Definition | Description | Causes and symptoms | Treatment

Definition

Thyroid cancer is a disease in which the cells of the thyroid gland become abnormal, grow uncontrollably and form a mass of cells called a tumor.

Description

The thyroid is a hormone-producing, butterfly-shaped gland located in the neck at the base of the throat. It has two lobes, the left and the right. The thyroid uses iodine, a mineral found in some foods, to make several of its hormones. Thyroid hormones regulate essential body processes such as heart rate, blood pressure , body temperature, metabolism, and affect the nervous system, muscles and other organs. These hormones play an important role in regulating childhood growth and development.

Types of thyroid cancer

Thyroid cancer is grouped into four types based on how cells appear under a microscope. The types are papillary, follicular, medullary and anaplastic thyroid cancers. They grow at different rates and can spread to other parts of the body if left untreated. The two most common types are papillary carcinoma and follicular carcinoma.

papillary The papillary type (60%–80% of all thyroid cancers) is a slow-growing cancer that develops in the hormone-producing cells containing iodine.

follicular The follicular type (30%–50% of thyroid cancers) also develops in the hormone-producing cells.

medullary The medullary type (5%–7% of all thyroid cancers) develops in the parafollicular cells (known as the C cells) that produce calcitonin, a hormone that does not contain iodine.

anaplastic The fourth type of thyroid cancer, anaplastic (2% of all thyroid cancers), is the fastest growing, most aggressive thyroid cancer type.

Alternatives

Diseases of the thyroid gland affect millions of Americans. The most common diseases of the thyroid are hyperthyroidism (Grave's disease) and hypothyroidism, an overactive or an underactive gland, respectively. Sometimes lumps or masses may develop in the thyroid. Although most (95%) of these lumps or nodules are non-cancerous (benign), all thyroid lumps should be taken seriously. The American Cancer Society estimates that in 2007, approximately 33,550 new cases of thyroid cancer were diagnosed in the United States.

Women are three times more likely to develop thyroid cancer than men. Unlike many cancers,thyroid cancers are most often diagnosed in younger people, with almost two-thirds of cases diagnosed in individuals between the ages of 20 and 55. Caucasians are affected more often than African Americans.

Causes and Symptoms

The exact cause of thyroid cancer is not known but some risk factors have been identified. Radiation was used in the 1950s and 1960s to treat acne and to reduce swelling in infections of the tonsils, adenoids and lymph nodes. It has been proven that this exposure is a risk factor for thyroidcancer. In some areas of the world, diets are low in iodine. Papillary and follicular cancers occur more frequently in these areas. Iodine deficiency is not a large problem in the United States because iodine is added to table salt and other foods. Approximately 7% of thyroid cancers are caused by the alteration (mutation) of a gene called the RET oncogene, which can be inherited.

Symptoms are rare, and the lump is not usually painful. The following are symptoms of thyroid nodules.

A lump or nodule that can be felt in the neck is the most frequent sign of thyroid cancer.

The lymph nodes may be swollen and the voice may become hoarse because the tumor presses on the nerves leading to the voice box.

Some patients experience a tight or full feeling in the neck and have difficulty breathing or swallowing.

Diagnosis

Physicians use several tests to confirm the suspicion of thyroid cancer, to identify the size and location of the lump and to determine whether the lump is non-cancerous (benign) or cancerous (malignant).

A blood test called the thyroid stimulating hormone (TSH) test checks thyroid function. Blood is drawn by a technician with a needle and the test takes a few minutes. Results take several days to be interpreted by a pathologist.

The calcitonin test may be ordered to evaluate calcitonin levels in blood. Calcitonin is a hormone produced by the C cells (parafollicular cells) of the thyroid gland. The hormone is produced in excess when the parafollicular cells of the thyroid become cancerous. Results of this test are used to confirm the diagnosis of medullary thyroid cancer if it is suspected.

Computed tomography (CT) scan or ultrasonography (an ultrasound scan) are imaging tests used to produce a picture of the thyroid. A radiologist usually interprets the Results of these tests within 24 hours. In ultrasonography, high-frequency sound waves are bounced off the thyroid. The pattern of echoes produced by these waves is converted into a computerized image on a television screen. This test can determine whether the lumps found in the thyroid are benign fluid-filled cysts or solid malignant tumors.

A radioactive scan (a thyroid nuclear medicine scan ) may take several hours and is used to identify abnormal areas in the thyroid. For this test, the patient is given a very small amount of radioactive iodine that can either be swallowed or injected. Since the thyroid is the only gland in the body that absorbs iodine, the radioactive iodine accumulates there. An x-ray image is taken or an instrument called a scanner is used to identify areas in the thyroid that do not absorb iodine normally. These abnormal spots are called cold spots and further tests are performed to check whether the cold spots are benign or malignant tumors. If a significant amount of radioactive iodine is concentrated in the nodule, then it is termed “hot” and is usually benign. A radiologist interprets the Results within a day.

The most accurate diagnostic tool for thyroid cancer is a biopsy. In this process, a sample of thyroid tissue is obtained and examined under a microscope by a pathologist. This usually takes a day. The tissue sample can be obtained either by drawing out a sample of tissue through a needle (needle biopsy) or by surgical removal of the nodule (surgical biopsy). A needle biopsy takes a few minutes and can be done by a trained physician, usually a radiologist. The surgical biopsy is done by a surgeon under general anesthesia with the help of an anesthesiologist and takes a few hours. If thyroid cancer is diagnosed, further tests may be done to determine the stage of the disease and help doctors plan appropriate treatment.

Staging

The aggressiveness of each type of thyroid cancer is different. Cancer staging considers the size of the tumor, whether it has grown into surrounding lymph nodes and whether it has spread to distant parts of the body (metastasized). Age and general health status are also taken into account. The American Joint Commission on Cancer (AJCC) staging is summarized below for each thyroid cancer type.

papillary and follicular In patients younger than 45 years:

Stage I: Patients without evidence of cancer beyond the thyroid.

Stage II: Patients with spread of cancer outside the thyroid gland to one or more distant sites.

In patients over 45:

Stage I: Tumors are smaller than 2 cm (0.3 in).

Stage II: Tumors are 2–4 cm (0.3–0.6 in) across but have not spread to adjacent lymph nodes or distant sites.

Stage III: Tumors have spread locally to nearby lymph nodes or are larger than 4 cm (0.6 in) and have grown slightly outside of the thyroid but not into lymph nodes or distant sites.

Stage IV: Tumors have spread outside the thyroid area (distant metastases).

In the case of Stage IV cancer, the places to which thyroid cancer often metastasizes are the lungs and bone.

medullary The stages of medullary thyroid carcinomas for individuals at any age are the same as for papillary or follicular thyroid cancer in people over age 45.

anaplastic All cases of anaplastic thyroid cancer are considered Stage IV because this type of cancer is extremely aggressive.

Treatment

Papillary thyroid cancer can be treated successfully. Follicular thyroid cancer also has a good cure rate but may be difficult to control if the cancer invades blood vessels or spreads to nearby structures in the neck. Medullary thyroid cancers are more difficult to control because they often spread to other parts of the body. Anaplastic thyroid cancer is the fastest growing and tends to respond poorly to all treatments.

Like most cancers, cancer of the thyroid is best treated when it is found early by a primary physician. Treatment depends on the type of cancer and its stage. The four types of treatment used are surgical removal, radiation therapy, hormone therapy, and chemotherapy .

Surgery

Surgical removal is the usual treatment if the cancer has not spread to distant parts of the body. It is the primary treatment for early stage papillary, follicular, and medullary thyroid cancers. The surgeon may remove the side or lobe of the thyroid where the cancer is found (lobectomy) or all of it (total thyroidectomy). If the adjoining lymph nodes are affected, they may also be removed during surgery.

Radiation

For papillary and follicular thyroid cancers, radioactive iodine may be used in addition to surgery. In this treatment, the patient is asked to swallow a drink containing radioactive iodine. Because the thyroid cells take up iodine, the radioactive iodine collects in any thyroid tissue remaining in the body and kills the cancer cells. External beam radiation may be used if the radioactive iodine is unsuccessful.

KEY TERMS

Calcitonin —A hormone produced by the parafollicular cells (C cells) of the thyroid. The main function of the hormone is to regulate calcium levels in body serum.

Chemotherapy —Treatment of cancer with synthetic drugs that destroy the tumor either by inhibiting the growth of cancerous cells or by killing them.

Hormone therapy —Treatment of cancer by inhibiting the production of hormones such as testosterone and estrogen.

Hyperthyroidism —A condition in which the thyroid is overactive due to overstimulation of the thyroid cells.

Hypothyroidism —A condition in which the thyroid gland is underactive.

Lobectomy —A surgical procedure that removes one lobe of the thyroid gland.

Radiation therapy —Treatment with high-energy radiation from x-ray machines, cobalt, radium, or other sources.

Total thyroidectomy —A surgical procedure that removes the entire thyroid gland.

For medullary cancers, radioactive iodine is not used. External beam radiation may be used as a palliative therapy. (A palliative therapy is one intended to make the patient more comfortable, not to cure the cancer.)

Hormone therapy

Removal of the thyroid gland causes levels of thyroid hormones to decrease. The pituitary gland then produces TSH, which normally stimulates the thyroid gland to make thyroid hormone. TSH stimulates thyroid cells to grow, and most likely promotes thyroid cancer growth. Hormone therapy uses hormones after surgery to stop this growth and the formation of new cancerous thyroid cells. To prevent cancerous growth, the natural hormones produced by the thyroid are taken in the form of a pill. This maintains normal hormone levels and inhibits the pituitary gland from making TSH. If the cancer has spread to other parts of the body and surgery is not possible, hormone treatment is aimed at killing or slowing the growth of cancer cells throughout the body.

Chemotherapy

For advanced thyroid cancers for which surgery was not an option or that have not responded well to other treatments, chemotherapy may be used. There is no standard chemotherapeutic regimen for advanced papillary, follicular, and anaplastic thyroid cancers. Clinical studies are ongoing for patients with these cancers. Anaplastic thyroid cancer may show an increased local response to the chemotherapeutic agent, doxorubicin, which is used as a radiation sensitizer in combination with hyperfractionated radiation therapy. Paclitaxel may provide some palliative benefit. Patients with anaplastic thyroid cancer may be eligible for ongoing clinical trials.

Clinical trials

As of 2008, approximately 50 clinical trials were in progress for patients diagnosed with various types of thyroid cancer. Information about current clinical trials is available through the National Institutes of Health.

Alternative and complementary treatments

Alternative treatments are treatments used instead of conventional treatments. Complementary therapies are intended to supplement traditional therapies and usually have the objective of relieving symptoms or helping cancer patients cope with the disease or traditional treatments. Common complementary therapies that may be employed by cancer patients are aromatherapy, art therapy, journal therapy, massage, meditation, music therapy, prayer , t'ai chi, and yoga or other forms of exercise , which can reduce anxiety and increase a patient's feeling of well-being. A well-balanced diet can also enhance a patient's sense of well-being, and can help patients with cancer better manage their treatments and the side effects of those treatments.

Prognosis

As of 2008, the five year relative survival rates for individuals with thyroid cancer are:

Papillary: Ranges from 100% in Stage I to 45% in Stage IV.

Follicular: Ranges from 100% in Stage I to 47% in Stage IV.

Medullary: Ranges from 100% in Stage I to 24% in Stage IV.

Anaplastic carcinomas: Approximately 3% since all tumors are classified as Stage IV.

QUESTIONS TO ASK YOUR DOCTOR

What type of thyroid cancer do I have?

Has it spread?

Is my thyroid cancer hereditary? Should other members of my family be tested?

What treatment do you recommend? Do you recommend a clinical trial?

What are the advantages, disadvantages, and side effects of this treatment?

How much experience do you have treating thyroid cancer/performing thyroid surgery?

Prevention

It is not possible to prevent this disease completely because most people with thyroid cancer have no known risk factor. The risk for radiation-related thyroid cancer can be reduced by avoiding radiation to the neck when possible. Inherited cases of medullary thyroid cancer can be prevented. If a family member has had this disease, other family members can be tested and treated early. Carriers of the RET mutation may want to consider a prophylactic thyroidectomy at an early age. The National Cancer Institute recommends that every one or two years, a doctor examine anyone who has received radiation to the head and neck during childhood. The neck and thyroid should be carefully examined for any lumps or enlargement of nearby lymph nodes. Ultrasound may be used to screen for the disease in people at risk for thyroid cancer.

Caregiver concerns

After thyroid surgery, some patients experience difficulty swallowing, voice changes, and damage to the parathyroid glands.

After surgery, swallowing may be difficult. Many patients start with soft foods, like milkshakes, bananas, applesauce, yogurt, mashed potatoes, and pureed foods. A consultation with a dietitian before surgery may be helpful, so that the patient can be prepared.

Hoarseness after surgery is usually temporary. Patients may have difficulty hitting high notes when singing, but the voice change and hoarseness is usually not a major issue for most patients. (Professional singers are advised to discuss their surgery in great detail with their surgeons beforehand.)

If all four parathyroid glands are injured or damaged, it may be necessary for patients to takecalcium supplements for a few weeks. Rarely, these supplements may be prescribed for longer periods of time, or even indefinitely.

After radioiodine treatment, some patients experience neck tenderness, nausea and stomach irritation, and dry mouth (xerostomia). These side effects are rare, but if they occur, patients can try to eat foods that are easy to digest, drink plenty of water to keep the mouth and throat moist, keep lips moist with lip balm, and suck on hard candies to alleviate dry mouth.

The side effects of chemotherapy are bone marrow suppression causing anemia and low platelets. This causes weakness or bleeding. Other problems are nausea and vomiting, hair loss (alopecia ), and inflammation of the oral mucosa. The symptoms are improved with medications.

Depression , if it occurs, is often temporary and can be managed by counseling and family support. Medication is usually not necessary.

Complications of surgery are rare with experienced surgeons. Sometimes injury to the nerves in the neck can cause voice changes. This can be improved with collagen injection after surgery. Occasionally, there is bleeding after surgery and the incision is reopened to evacuate the clot and stop the bleeding. Patients may have a slightly increased risk of developing another cancer (such as leukemia) in the future after undergoing radioiodine treatment, but this correlation has not been proven. Because thyroid cancers may grow slowly and may recur decades after treatment, follow-up care is important.

Resources

BOOKS Cameron, John L. Current Surgical Therapy. 6th ed. St. Louis: Mosby, Inc., 2001.

ORGANIZATIONS

American Cancer Society. (800) ACS-2345. http://www.cancer .org.

National Cancer Institute, Cancer Information Service. (800) 4-CANCER (800-422-6237). TTY: (800) 332-8615. http://www.nci.nih.gov/.

OTHER

Clinical Trials. National Cancer Institute (NCI). http://www.cancer .gov/clinicaltrials.

Eating Hints for Cancer Patients: Before, During, and After Treatment. National Institutes of Health. NIH Publication #98-2079. Revised July 1997. Also available at:http://cancernet.nci.nih.gov/cancertopics/eatinghints.pdf.

How is Thyroid Cancer Staged? American Cancer Society (ACS). October 3, 2007 [cited March 24, 2008]. http://www.cancer.org/docroot/CRI/content/CRI_2_4_3X_How_is_thyroid_cancer_staged_43.asp?sitearea=.

Practice Guidelines in Oncology Thyroid Cancer v.2.2007. National Comprehensive CancerNetwork (NCCN). April 20, 2007 [cited March 24, 2008].http://www.nccn.org/professionals/physician_gls/PDF/thyroid.pdf.