|
|
 When normal cells are damaged or old they undergo apoptosis; cancer cells, however, avoid apoptosis |
Cancer is a class of diseases characterized by uncontrolled cell division and the ability of these cells to invade other tissues, either by direct growth into adjacent tissue (invasion) or by migration of cells to distant sites (metastasis). This unregulated growth is caused by a series of acquired or inherited mutations to DNA within cells, damaging genetic information that define the cell functions and removing normal control of cell division. These invasive tissues are said to be malignant. The word tumor ("swelling" in Latin) refers to any mass of abnormal tissue, but may be either malignant (cancerous) or benign (noncancerous).
Cancer can cause many different symptoms, depending on the site and character of the malignancy and whether there is metastasis (spread). A definitive diagnosis usually requires the microscopic examination of tissue in the form of a biopsy. Once diagnosed, cancer is usually treated with surgery, chemotherapy and/or radiation. If untreated, most cancers eventually cause death; cancer is one of the leading causes of death in developed countries. Most cancers can be treated and many cured, especially if treatment begins early. Many forms of cancer are associated with environmental factors that are avoidable. Smoking tobacco leads to more cancers than any other environmental factor. |