thyroid cancer

Thyroid Cancer

 

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

Thyroid cancer is grouped into four types based on how its 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 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 also play an important role in regulating childhood growth and development.

Diseases of the thyroid gland affect millions of Americans. The most common diseases of the thyroid are either hyperthyroidism (Graves' disease) or hypothyroidism, an overactive or an underactive gland, respectively. Sometimes lumps or masses may develop in the thyroid, and although most (ninety-five percent) of these lumps or nodules are noncancerous (benign), all thyroid lumps should be taken seriously. The American Cancer Society estimates that the approximately 17,200 new cases of thyroid cancer that occur in the United States account for 1% of all cancers.

Women are three times more likely to develop thyroid cancer than men. Although the disease affects teenagers and young adults, most people that develop thyroid cancer are over 50 years of age.

Causes and symptoms

The exact cause of thyroid cancer is not known; but it is more common in whites than in African Americans. 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 thyroid cancer. 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 cancer are caused by the alteration (mutation) of a gene called the RET gene, which can be inherited.

Symptoms are rare so the lump is not usually painful. The symptoms of thyroid nodules are:

• 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 noncancerous (benign) or cancerous (malignant). Blood tests such as the thyroid stimulating hormone (TSH) test check thyroid function. These are drawn by a technician with a needle and takes a few minutes. It take several days to be interpreted by a pathologist. Calcitonin is produced by the C cells (parafollicular cells) of the thyroid gland when the parafollicular cells of the thyroid become cancerous. Blood calcitonin levels are used to confirm the diagnosis of medullary thyroid cancer if it is suspected.

Computed tomography scan (CT scan) or an ultrasonography (ultrasound scan) are imaging tests used to produce a picture of the thyroid and usually last less than one hour. A radiologist usually interprets the results within 24 hours. In ultrasonography, high-frequency sound waves are bounced off the thyroid. The pattern of echoes that is 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 may take several hours and can be used to identify any abnormal areas in the thyroid by giving the patient a very small amount of radioactive iodine, which can either be swallowed or injected into the thyroid. Since the thyroid is the only gland in the body that absorbs iodine, the radioactive iodine accumulates there. An x-ray image can then be taken or an instrument called a "scanner" can be 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. Again 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 withdrawn and examined under a microscope by a pathologist. This usually takes a day or so. The tissue samples 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 any trained physician, usually a radiologist. The surgical biopsy is done by a surgeon under general anesthesia with the help of an anesthesiologist and will take a few hours. If thyroid cancer is diagnosed, further tests may be done to learn about the stage of the disease and help doctors plan appropriate treatment.

Treatment

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. In patients less than 45 years old there are only two stages. I papillary or follicular type thyroid cancer, stage I refers to patients without evidence of cancer that has spread to the body. Stage II refers to patients with spread of cancer outside the thyroid gland. In patients over 45, patients with tumors smaller than one cm are classified as stage I, those with tumors not broken through the capsule (covering) of the thyroid belong to stage II, those with tumors outside the capsule or lymph node involvement are called stage III and those with spread outside the thyroid area are stage IV. In medullary—type thyroid cancer, stage I and IV are the same. Stage II consists of patients with tumors greater than one cm and stage III comprises patients with lymph node involvement.

The papillary type (60-80% of all thyroid cancers) is a slow-growing cancer that develops in the hormone-producing cells (that contain iodine) and can be treated successfully. The follicular type (30-50% of thyroid cancers) also develops in the hormone-producing cells, has a good cure rate but may be difficult to control if the cancer invades blood vessels or grows into nearby structures in the neck. The medullary type (5-7% of all thyroid cancers) develops in the parafollicular cells (also known as the C cells) that produce calcitonin, a hormone that does not contain iodine. Medullary thyroid cancers are more difficult to control because they often spread to other parts of the body. The fourth type of thyroid cancer, anaplastic (2% of all thyroid cancers), is the fastest-growing and is usually fatal because the cancer cells rapidly spread to the different parts of the body.

More than 90% of patients who are treated for papillary or follicular cancer will live for 15 years or longer after the diagnosis of thyroid cancer. Eighty percent of patients with medullary thyroid cancer will live for at least 10 years after surgery. Only 3-17% of patients with anaplastic cancer survive for five years.

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. Four types of treatment are used: surgical removal, radiation therapy, hormone therapy and chemotherapy. Surgical removal is the usual treatment if the cancer has not spread to distant parts of the body.

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. When the thyroid gland is removed and levels of thyroid hormones decrease, the pituitary gland starts to produce TSH that stimulates the thyroid cells to grow.

A radiation-oncologist uses radiation therapy with high-energy x-rays to kill cancer cells and shrink tumors. The radiation may come from a machine outside the body (external beam radiation), or the patient may be 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. A hematologist-oncologist uses chemotherapy either as a pill or an injection through a vein in the arm.

Alternative treatment

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 that are produced by the thyroid are taken in the form of pills. Thus, their levels remain normal and inhibit 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.

Key terms

Biopsy — The surgical removal and microscopic examination of living tissue for diagnostic purposes.

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 the 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.

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.

A powerful phytochemical, lycopene, gives tomatoes their red color and appears to act as an antioxidant in the body, repairing damaged cells and scavenging free radicals, the molecules responsible for most types of degenerative diseases and aging. Antioxidants such as lycopene help inhibit DNA oxidation, which can lead to certain forms of cancer. Lycopene is a normal constituent of human blood and tissues, where it is found in greater concentrations than beta-carotene or any other carotenoid. Tomatoes, including cooked or processed tomatoes, tomato juices, soups, sauces, paste and ketchup, contain more lycopene than any other food. Guava, rose hip, watermelon and grapefruit also contain lycopene.

Other antioxidants are: vitamin E (Dosage: 400 IU daily), vitamin C (Dosage: 1,000 to 4,000 mg daily), beta carotene (Dosage: 15 mg (25,000 IU) daily), lutein (Dosage: 6 to 20 mg daily), pycnogenol (Dosage: 25 to 50 mg daily), green tea (Dosage: 300 to 400 mg of green tea polyphenols daily), grape-seed extract (Dosage: 100 mg daily), alpha lipoic acid (Dosage: 50 to 200 mg daily), N-acetylcysteine (Dosage: 600 mg daily) and selenium (Dosage: 200 to 400 mcg daily). Pregnant women should consult a physician before taking any medication.

Prevention

Because most people with thyroid cancer have no known risk factor, it is not possible to completely prevent this disease. However, inherited cases of medullary thyroid cancer can be prevented and radiation to the neck is avoided. If a family member has had this disease, the rest of the family can be tested and treated early. The National Cancer Institute recommends that a doctor examine anyone who has received radiation to the head and neck during childhood at intervals of one or two years. The neck and the thyroid should be carefully examined for any lumps or enlargement of the nearby lymph nodes. Ultrasound may also be used to screen for the disease in people at risk for thyroid cancer.

Resources

Organizations

National Cancer Institute (National Institutes of Health). 9000 Rockville Pike, Bethesda, MD 20892. (800) 422-6237. http://www.nci.nih.gov.

Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.

thyroid cancer

A general term for a malignant epithelial lesion of the thyroid with 45,000 new cases/year (US), and 1700 deaths. Women account for three-fourths of cases; current, overall 5-year survival with treatment is 95+%. Carcinoma of the thyroid is divided into histologically—and usually clinically—distinct subtypes in order of increasing aggressiveness: papillary carcinoma, follicular carcinoma, medullary carcinoma, poorly differentiated and undifferentiated (anaplastic) carcinoma.

Clinical
Palpable neck mass (0.14% of all palpable neck masses ultimately prove to be TC).
 
Prognosis
Uncertain; the initial (5-year) prognosis depends on the histological subtype, but may recur decades later; administration of TSH stimulates remaining thyroid tissue and prevents symptomatic hypothyroidism, which occurs when thyroid hormone is discontinued, and stimulates radioiodine uptake by residual normal and cancerous thyroid tissue.

Staging, carcinoma of thyroid
pTX—Primary tumour cannot be assessed.
pT0—No evidence of primary tumour.
pT1a— = 10 mm limited to thyroid.
pT1b— = 20 mm, > 10 mm limited to thyroid.
pT2—> 20 mm, ≤ 40 mm limited to thyroid.
pT3—> 40 mm limited to thyroid or any tumour with minimal extrathyroidal extension—e.g. extension to sternothyroid muscles or perithyroid soft tissues.

All anaplastic carcinomas are considered pT4 tumours:
pT4a—Tumour invades beyond thyroid capsule and invades any of: subcutaneous soft tissues, larynx, trachea, oesophagus, recurrent laryngeal nerve.
pT4b—Tumour invades prevertebral fascia, mediastinal vessels or encases carotid artery.

Multifocal tumours (= 2 foci) of all histological types should be designated (m), the largest focus determining the classification—e.g., pT2(m).

pNX—Cannot assess regional lymph nodes.
pN0—No regional nodes involved.
pN1a—Metastasis in level-VI (pretracheal, paratracheal and prelaryngeal/Delphian) lymph nodes.
pN1b—Metastasis in other unilateral, bilateral or contralateral cervical (levels I, II, III, IV or V), or retropharyngeal or superior mediastinal lymph nodes.

M1—Distant metastases proven histologically (MX is not used in TNM v7, which itconsiders as proof that M0 cannot be arrived at by surgical pathology alone).

RX—Cannot assess presence of residual primary tumour.
R0—No residual primary tumour.
R1—Microscopic residual primary tumour.
R2—Macroscopic residual primary tumour.

Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.

thyroid cancer

Thyroid carcinoma Oncology A malignant epithelial lesion of the thyroid that affects 14,000/yr–US, 1100 deaths/yr; ♀ account for 77% of new cases and 61% of deaths; current overall 5-year survival with treatment is 95% Risk factors Persons exposed to the upper body–especially head & neck radiation during childhood; persons with a family Hx of TC or MEN 2 syndrome; the risk of radiation-induced thyroid nodularity and CA ↑ with radiation dose and ↓ the older the person was at the time of irradiation; medullary TC, which comprises about 10% of all TCs, is inherited in 25% of cases as part of  MEN 2 syndrome Clinical Palpable neck mass Note 0.14% of palpable neck masses ultimately prove to be TC Management Surgery, radioiodine Prognosis Uncertain; recurrences may occur decades later; administration of TSH stimulates remaining thyroid tissue, and prevents symptomatic hypothyroidism, which occurs when thyroid hormone is discontinued, and stimulates radioiodine uptake by residual thyroid and thyroid CA tissue. See Thyrotropin.

McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.