Thyroid cancer is a disease in which the thyroid cells become abnormal, growuncontrollably, and form tumors. The thyroid is a butterfly-shaped gland, located at the base of the throat. It has two lobes, the left and the right. Thethyroid gland makes hormones that regulate heart rate, blood pressure, bodytemperature, and metabolism. The hormones produced by the thyroid alsoaffect the nervous system, muscles, and other organs, and play an important role in regulating childhood growth and development. The thyroid usesiodine, a mineral found in some foods, to make several of its hormones.
Thyroid cancers are grouped into four types, depending on how the cells lookunder the microscope. The four types are papillary, follicular, medullary, and anaplastic thyroid cancers. The cancers grow at different rates, so the aggressiveness of each cancer is different. Papillary and follicular cancer develops in the cells that produce thyroid hormones containing iodine. About 60-80% of all thyroid cancers are papillary cancers. Medullary cancers develop in the parafollicular cells (also known as the C cells) which produce the calcitonin hormone. These cancers have a tendency to spread to other partsof the body and hence are difficult to control. Anaplastic cancer is the fastest growing of all thyroid cancers and is usually fatal.
Exposure to radiation during childhood is a known risk factor for thyroid cancer. In areas of the world where people's diets are low in iodine, papillaryand follicular cancers occur more frequently. In the United States, dietary iodine is plentiful because it is added to table salt and other foods.
The most frequent symptom of thyroid cancer is a lump or nodule that can be felt in the neck. The lymph nodes may be swollen and the voice may become hoarse because the tumor presses on the nerves leading to the voice box.
The doctor may use several tests to confirm a diagnosis of thyroid cancer. Blood tests, such as the thyroid stimulating hormone (TSH) test, may be orderedto check how well the patient's thyroid is functioning. An ultrasound scan,may be used to produce a picture of the thyroid. This test can determine whether the lumps found in the thyroid are fluid-filled cysts or solid malignanttumors.
A radioactive scan is used to identify abnormal areas in the thyroid. The patient is given a very small amount of radioactive iodine, which can either betaken by mouth or injected into the thyroid. Since the thyroid is the only gland in the body that absorbs iodine, the radioactive iodine accumulates there. A x-ray image can then be taken 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. The most accurate diagnostic tool for thyroid cancer is a biopsy. In this process, a sample of thyroid tissue is withdrawn and examined undera microscope.
Treatment for thyroid cancer depends on the type of cancer and its stage. Four types of treatment are used: surgical removal, radiation therapy, hormone therapy, and che-mo-ther-a-py.
If the cancer has not spread to distant parts of the body, surgical removal is the usual treatment. The surgeon may remove the side or lobe of the thyroidwhere the cancer is found (lobectomy) or all of it (total thyroidectomy). Radiation therapy uses high-energy x rays to kill cancer cells and shrink tumors. Because the thyroid cells are the only cells of the body that take up iodine, the radioactive iodine collects in any thyroid tissue remaining in the body and kills the cancer cells. Chemotherapy is used if the cancer has spreadto other parts of the body and surgery is not possible. This treatment is aimed at killing or slowing the growth of cancer cells throughout the body.
Hormone therapy uses hormones to stop the cancer cells from growing. When thethyroid gland is removed and levels of thyroid hormones fall, the pituitarygland starts producing a hormone called "thyroid stimulating hormone" (TSH).TSH stimulates the thyroid cells to grow. This stimulation would also inducegrowth of the cancerous thyroid cells. To prevent this, the natural hormonesthat are produced by the thyroid are taken in the form of pills. Thus, theirlevels remain normal and inhibit the pituitary from making TSH.
Like most cancers, cancer of the thyroid is best treated when it is found early. Patients who are treated for papillary, follicular cancer or medullary thyroid cancer have an excellent rate of survival. Eighty to 90% of patients will live for at least 10 years after surgery. The fourth type of thyroid cancer, anaplastic, is usually fatal. Only 3-17% of patients with this cancer survive for 5 years.
Because most people with thyroid cancer have no known risk factor, it is notpossible to completely prevent this disease. The National Cancer Institute recommends that a doctor examine anyone who has received radiation to the headand neck during childhood at intervals of one or two years. The neck and thethyroid should be carefully examined for any lumps or enlargement of the nearby lymph nodes. Ultrasonography may be used for people at risk for thyroid cancer.