The thyroid is a gland below the Adam's apple and just above the breastbone. It is u-shaped and has two lobes, one on either side of the windpipe. Cancer of this organ accounts for only 1 percent of all malignancies and 0.2 percent of cancer deaths. The American Cancer Society estimates that in 2000 about 18,400 new cases of thyroid cancer will be diagnosed in the United States. This cancer occurs twice as often in women as in men and more often in whites than in African-Americans. Of the new cases, about 13,700 will occur in women, and 4,700 in men. An estimated 700 women and 500 men will die of thyroid cancer in 2000. Thyroid cancer generally affects people between the ages of 25 and 65.
The thyroid gland absorbs iodine from the bloodstream so it can produce thyroid hormone, which affects all tissues and regulates the body's metabolism. The thyroid gland contains two types of cells: follicle cells make and store thyroid hormone and a protein called thyroglobulin, while C-cells make the hormone calcitonin. The type of cell determines the type of thyroid cancer, which in turn determines the extent of the cancer and the type of treatment needed.
Many types of tumors can develop in the thyroid gland, of which 95 percent are benign, or non-cancerous. Tumors often appear as nodules, or bumps in the neck. Thyroid nodules can develop at any age, but they are most common in adults. Often people find these bumps by seeing or feeling them or they are detected during a routine medical exam.
Although these nodules are not often cancerous, they can still affect bodily functions. For example, hyperplastic nodules or adenomas make too much thyroid hormone, resulting in nervousness, heart palpitations, sweating and weight loss.
Less than 5 percent of thyroid nodules are cancerous, and these are defined as well differentiated or undifferentiated. Well-differentiated tumors look more like normal tissue, while undifferentiated cancers do not.
For specific information on types of cancers of organs close to the thyroid gland or that frequently spread to this organ, please see the summaries on multiple endocrine neoplasia, adrenocortical carcinoma and parathyroid cancer.
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