Thyroid Cancer

The thyroid gland is the gland that makes and stores hormones that help regulate the heart rate, blood pressure, body temperature, and metabolism. Thyroid hormones are essential for the function of every cell in the body. They help regulate growth and the rate of chemical reactions in the body. Thyroid hormones also help children grow and develop. The thyroid gland is located in the lower part of the neck, below the Adam's apple, wrapped around the trachea. It has the shape of a butterfly with two lobes attached to one another by a middle part called the isthmus. The thyroid uses iodine, a mineral found in some foods and in iodized salt, to make its hormones. The two most important thyroid hormones are thyroxine (T4) and triiodothyronine (T3). The thyroid gland also makes the hormone calcitonin, which is involved in calcium metabolism and stimulating bone cells to add calcium to bone.

Thyroid caner is a disease in which the cells of the thyroid gland become abnormal, grow uncontrollably and form a mass of cells called a tumor. Some tumors grow and enlarge only at the site where they began. These types of tumors are referred to as benign tumors. Other tumors not only enlarge locally, but they also have the potential to invade and destroy the normal tissues around them and to spread to other regions of the body. These types of tumors are called malignant tumors or cancer.() Malignant tumors of the thyroid gland tend to develop gradually and remain localized. The tumors usually appear as nodules or lumps of tissue growing on or inside the gland itself. Almost 95% of these lumps or nodules are non-cancerous (benign), and are usually caused by thyroid conditions such as goiters (Shin 422). The American Cancer Society estimates that there will be about 23,600 new cases of thyroid cancer in the U.S. in 2004 (Thackery 1057). Women are three times more likely to develop thyroid cancer than men. Although the disease also affects younger people, most people who develop thyroid cancer are over 50 years of age. Caucasians are affected more often than African-Americans (Rubin 88).

There are four main types of thyroid cancers: papillary, follicular, medullary, and anaplastic. These tumors are identified by the type of cells seen under the microscope. Papillary thyroid tumors occur most often. This type of thyroid cancer develops on one or both sides of the gland and remains confined for several years and accounts for 60% - 80% of all thyroid cancers (Thackery 1057). Follicular tumors, on the other hand, grow only on one side of the gland. These tumors develop in the hormone-producing cells and account for 30% - 50% of all thyroid cancers (Thackery 1057). Medullary thyroid tumors account for 5% - 7% of all thyroid cancers, and are usually uncommon. Like papillary tumors, they grow on one or both sides of the gland. Anaplastic tumors, though extremely rare, develop on either side of the thyroid gland and spread rapidly to other parts of the body. It account for only 2% of all thyroid cancers but is the fastest growing, and most aggressive thyroid cancer type (Thackery 1057).

The aggressiveness of each type of thyroid cancer is different. There are four main stages in each of the types of thyroid cancer except for anaplastic cancer (Rubin 91). In the stage I of papillary and follicular thyroid cancer, the cancer is located only in the thyroid and may be found in one or both of the lobes. In stage II if the patients are younger than 45 years of age, the cancer has spread beyond the thyroid. But if the patient is older than 45 years of age, the cancer is only in the thyroid and is larger than 1 centimeter. In stage III, the cancer is usually found in patients older than 45 years of age and has spread outside of the thyroid or has spread to the lymph nodes but not outside of the neck. In stage IV, the cancer is again usually found in patients over the age of 45. It most likely has spread to other parts of the body such as the lungs or bones (Thackery 1058). Medullary thyroid cancer is quite uncommon. In stage I, the is located in one or both of the thyroid glands and is about 1 centimeter in size, but throughout the last three stages of medullary thyroid cancer, the tumor grows by 1-4 centimeters and continuously spreads to other parts of the body (Shin 93). There is no staging system for anaplastic cancer of the thyroid. This cancer is located in either of the lobes and spreads faster than any of the other types (Thackery 1058).

The exact cause of thyroid cancer is not known but some risk factors have been identified. From the early 1950's to the late 1960's, thousands of children received radiation to treat acne and to reduce infection of the tonsils, adenoids and lymph nodes (Shin 419). It has been proven that radiation is a risk factor for thyroid cancer. Another risk factor is diets that are low in iodine. In parts of the world that have low iodine diets papillary and follicular