Ans. : The thyroid is a gland in the neck. It has two kinds of cells that make hormones. Follicular cells make thyroid hormone, which affects heart rate, body temperature, and energy level. C cells make calcitonin, a hormone that helps control the level of calcium in the blood.

The thyroid is shaped like a butterfly and lies at the front of the neck, beneath the voice box (larynx). It has two parts, or lobes. The two lobes are separated by a thin section called the isthmus.

A healthy thyroid is a little larger than a quarter. It usually cannot be felt through the skin. A swollen lobe might look or feel like a lump in the front of the neck. A swollen thyroid is called a goiter. Most goiters are caused by not enough iodine in the diet. Iodine is a substance found in shellfish and iodized salt.

Ans. : The definition of a tumor is a mass of abnormally growing cells. Tumors can be either benign or malignant. Benign tumors have uncontrolled cell growth, but without any invasion into normal tissues and without any spread. A malignant tumor is called cancer when these tumor cells gain the propensity to invade tissues and spread locally as well as to distant parts of the body. In this sense, thyroid cancer occurs when cells of the thyroid gland grow uncontrollably to form tumors that can invade the tissues of the neck, spread to the surrounding lymph nodes, or to the bloodstream and then to other parts of the body. The most common types of cancers of the thyroid gland are derived from the cells responsible for thyroid hormone production. The general term for cancers that come from glandular tissue is adenocarcinoma. In the thyroid, the most common types of cancer are papillary adenocarcinoma of the thyroid (75-80%) and follicular adenocarcinoma of the thyroid (˜15%). Papillary thyroid cancer takes on a folded appearance under the microscope, which eases its diagnosis. Follicular thyroid cancer may closely resemble normal thyroid tissue, but as a malignancy, has a propensity to divide uncontrollably and invade and spread. The next most common type of cancer of the thyroid is called medullary thyroid cancer (5%), which is derived from the parafollicular cells of the thyroid. This is often associated with a familial genetic predisposition to develop certain types of cancers (see below). The other major type of thyroid cancer often described is called anaplastic thyroid cancer (2%). This cancer usually affects older people and is very aggressive. Other types of cancers, such as lymphomas (cancer of the lymph gland cells), sarcomas (cancer of soft tissues such as muscle or cartilage cells), or metastases (cancers from other sites that have spread to the thyroid gland) are also seen in the thyroid gland.

The following are the major types of thyroid cancer:

* Papillary and follicular thyroid cancers account for 80 to 90 percent of all thyroid cancers. Both types begin in the follicular cells of the thyroid. Most papillary and follicular thyroid cancers tend to grow slowly. If they are detected early, most can be treated successfully.

* Medullary thyroid cancer accounts for 5 to 10 percent of thyroid cancer cases. It arises in C cells, not follicular cells. Medullary thyroid cancer is easier to control if it is found and treated before it spreads to other parts of the body.

* Anaplastic thyroid cancer is the least common type of thyroid cancer (only 1 to 2 percent of cases). It arises in the follicular cells. The cancer cells are highly abnormal and difficult to recognize. This type of cancer is usually very hard to control because the cancer cells tend to grow and spread very quickly.

Ans. : No one knows the exact causes of thyroid cancer. Doctors can seldom explain why one person gets this disease and another does not. However, it is clear that thyroid cancer is not contagious. No one can "catch" cancer from another person.

Research has shown that people with certain risk factors are more likely than others to develop thyroid cancer. A risk factor is anything that increases a person's chance of developing a disease.

The following risk factors are associated with an increased chance of developing thyroid cancer:

* Radiation. People exposed to high levels of radiation are much more likely than others to develop papillary or follicular thyroid cancer.

One important source of radiation exposure is treatment with x-rays. Between the 1920s and the 1950s, doctors used high-dose x-rays to treat children who had enlarged tonsils, acne, and other problems affecting the head and neck. Later, scientists found that some people who had received this kind of treatment developed thyroid cancer. (Routine diagnostic x-rays—such as dental x-rays or chest x-rays—use very small doses of radiation. Their benefits nearly always outweigh their risks. However, repeated exposure could be harmful, so it is a good idea for people to talk with their dentist and doctor about the need for each x-ray and to ask about the use of shields to protect other parts of the body.)

Another source of radiation is radioactive fallout. This includes fallout from atomic weapons testing (such as the testing in the United States and elsewhere in the world, mainly in the 1950s and 1960s), nuclear power plant accidents (such as the Chornobyl [also called Chernobyl] accident in 1986), and releases from atomic weapons production plants (such as the Hanford facility in Washington state in the late 1940s). Such radioactive fallout contains radioactive iodine (I-131). People who were exposed to one or more sources of I-131, especially if they were children at the time of their exposure, may have an increased risk for thyroid diseases.

People who are concerned about their exposure to radiation from medical treatments or radioactive fallout may wish to ask the Cancer Information Service at 1-800-4-CANCER about additional sources of information.

* Family history. Medullary thyroid cancer can be caused by a change, or alteration, in a gene called RET. The altered RET gene can be passed from parent to child. Nearly everyone with the altered RET gene will develop medullary thyroid cancer. A blood test can detect an altered RET gene. If the abnormal gene is found in a person with medullary thyroid cancer, the doctor may suggest that family members be tested. For those found to carry the altered RET gene, the doctor may recommend frequent lab tests or surgery to remove the thyroid before cancer develops. When medullary thyroid cancer runs in a family, the doctor may call this "familial medullary thyroid cancer" or "multiple endocrine neoplasia (MEN) syndrome." People with the MEN syndrome tend to develop certain other types of cancer.

A small number of people with a family history of goiter or certain precancerous polyps in the colon are at risk for developing papillary thyroid cancer.

* Being female. In the United States, women are two to three times more likely than men to develop thyroid cancer.

* Age. Most patients with thyroid cancer are more than 40 years old. People with anaplastic thyroid cancer are usually more than 65 years old.

* Race. In the United States, white people are more likely than African Americans to be diagnosed with thyroid cancer.

* Not enough iodine in the diet. The thyroid needs iodine to make thyroid hormone. In the United States, iodine is added to salt to protect people from thyroid problems. Thyroid cancer seems to be less common in the United States than in countries where iodine is not part of the diet.

Ans. : By far, the most common presentation of thyroid cancer is a solitary nodule on the thyroid, which can be felt on physical exam. As the thyroid gland is a fairly superficial organ in the neck, a thyroid nodule could be noticed early, at which time medical attention should be sought. By no means is every thyroid nodule a thyroid cancer. In fact, most represent hyperplasia (benign growth of the thyroid) of the thyroid gland.
The thyroid cancer can present as multiple nodules in the thyroid or a large mass in the neck. The large mass can be located either in the region of the thyroid, representing the primary thyroid cancer, or in a separate region of the neck, representing a spread of cancer to the lymph nodes. Thyroid tumors can also at times present as hoarseness or with symptoms of tracheal or esophageal compression, such as shortness of breath, air hunger, problems or pain with swallowing, or neck pain.