* Cancer can occur at any age, but mostly appears in people middle-aged and older. * Cancer causes more deaths in American children aged one to 14 years than any other disease. * In the 1980s more than 4.5 million Americans died from cancer. * About 83 million people alive today--or one in three Americans--will eventually get cancer. * Cancer cost the United States roughly $104 billion in 1990--including medical expenses and loss of work productivity. * Approximately 520,000 Americans die of cancer each year. The millions of cells that make up the body normally reproduce in an orderly manner, replacing worn-out tissues and repairing injuries to maintain health. However, certain cells may begin to reproduce abnormally, massing together to form tumors. If a tumor is benign, it will remain self-contained. A malignant--or cancerous--tumor, on the other hand, will invade neighboring tissues, and can spread through the blood and lymphatic systems to distant parts of the body in a process called metastasis.
Cancer is a class of diseases or disorders characterized by uncontrolled division of cells and the ability of these cells to invade other tissues, either by direct growth into adjacent tissue through invasion or by implantation into distant sites by metastasis. Metastasis is defined as the stage in which cancer cells are transported through the bloodstream or lymphatic system. Cancer may affect people at all ages, but risk tends to increase with age, due to the fact that DNA damage becomes more apparent in aging DNA. It is one of the principal causes of death in developed countries. There are many types of cancer. Severity of symptoms depends on the site and character of the malignancy and whether there is metastasis. A definitive diagnosis usually requires the histologic examination of tissue by a pathologist. This tissue is obtained by biopsy or surgery. Most cancers can be treated and some cured, depending on the specific type, location, and stage. Once diagnosed, cancer is usually treated with a combination of surgery, chemotherapy and radiotherapy. As research develops, treatments are becoming more specific for the type of cancer pathology. Drugs that target specific cancers already exist for several cancers. If untreated, cancers may eventually cause illness and death, though this is not always the case. The unregulated growth that characterizes cancer is caused by damage to DNA, resulting in mutations to genes that encode for proteins controlling cell division. Many mutation events may be required to transform a normal cell into a malignant cell. These mutations can be caused by chemicals or physical agents called carcinogens, by close exposure to radioactive materials, or by certain viruses that can insert their DNA into the human genome. Mutations occur spontaneously, and may be passed down from one generation to the next as a result of mutations within germ lines.
