| Cancer is a general term that is used to identify tissue that grows abnormally fast and that loses any specialized characteristics of the tissue from which it has arisen. Cancerous tumors tend to grow in an unrestricted fashion and expand into surrounding tissues and organs. Cells from a malignant neoplasm can separate from the initial tumor, travel to a different site (usually via the bloodstream or lymphatic system), and then start dividing to form a new, secondary tumor (metastasis).
Cancer usually develops in major organs such as the lungs, breasts, intestines, pancreas, lymphatic system (Hodgkin's and non-Hodgkin's lymphoma), the prostate gland in men, and the ovaries in women. Other sites of cancer formation include the urinary bladder, skin, mouth, lips, throat, kidney, thyroid, esophagus, brain, adrenal gland, stomach, and in women, the uterus. Malignant neoplasms can also develop in the blood cell-forming tissues located in the bone marrow (leukemia).
It is usually not known what causes cancerous cells to begin growing. One possible mechanism is that cancer-causing agents (carcinogens) may act on certain genes (oncogenes) within the cell to trigger mutations. The change in oncogenes is then passed on to all offspring cells, which divide more rapidly than the normal surrounding cells. Usually, the offspring cells show abnormal physical characteristics, including lack of differentiation, so they no longer perform the specialized task that they were meant to do. Because they escape the controls that keep them from growing abnormally, a cancerous tumor can form. It may take years before the tumor becomes large enough to cause symptoms, so by the time of discovery, the cancer may have metastasized to other vital organs such as the liver, lungs, bones, or brain.
Treatment of cancer is guided by staging. Staging helps determine the cancer's size, location and if it has invaded lymph nodes and other organs. Staging not only helps determine treatment but it also affects prognosis. A more localized cancer can be treated with surgery but a cancer that has mestasized is difficult to surgically remove. For more specific information on treatment see cancer of the bladder, lung, ovary, thyroid, kidney, brain, prostate, breast, bone, cervix, colon, esophagus, liver, oropharynx, oral cavity, pancreas, pleura, rectum, skin, small intestine, stomach, testicle, Hodgkin's lymphoma, non-Hodgkin's lymphoma, Multiple Myeloma and Hepatic Angiosarcoma.Risk: Risk factors for cancer include cigarette smoking or the use of smokeless tobacco; a diet that is high in fat or calories, or low in fiber or calcium; high alcohol consumption; low physical activity; obesity; occupational carcinogens such as asbestos, pesticides, hair dressing compounds, soot, tar, formaldehyde, vinyl chloride, and wood dusts; in women, certain reproductive and sexual factors such as early age at first menstruation (menarche), late age at menopause, never having been pregnant (nulliparity) or not carrying a pregnancy beyond 6 months, late first pregnancy (35 years or older); multiple sexual partners; infection with certain viruses (hepatitis B and C, human papillomavirus, Epstein-Barr virus, human immunodeficiency virus or HIV) or other biological agent (Schistosoma, Helicobacter pylori); radiation; anti-cancer drugs; hormones (estrogen, androgenic steroids); advanced age; and low socioeconomic status. Sex may predispose some individuals to some types of cancer. There may also be a genetic tendency to certain types of cancers within family groups. Incidence and Prevalence: Cancer is second only to heart disease as the leading cause of death in the US. |