Cancer is a general term used to identify tissue that grows abnormally fast and that loses any specialized characteristics of the tissue from which it has arisen. Cancer tumors (malignant neoplasms) 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 and replicating themselves 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 lymphomas), 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 (leukemias).
It is not completely clear what causes cells to become cancerous and begin growing in an uncontrolled fashion. One possible mechanism is that cancer-causing agents (carcinogens) may act on certain genes (oncogenes) within cells to trigger gene 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 cancer cells escape the controls that keep healthy cells from growing abnormally, a malignant 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 spread (metastasized) to other vital organs such as the liver, lungs, bones, or brain.
Treatment of cancer is guided by staging the disease through the examination of cells from affected tissue, the surrounding area, and areas of possible metastasis. Staging helps to determine the tumor size, location and if the cancer has invaded lymph nodes and other organs. Stages are expressed numerically as I, II, III, or IV, and described as "localized," "regional," and "distant." Staging not only helps determine treatment, but it also affects prognosis. Generally, the lower the numerical stage, the more likely that treatment will have a good outcome. A more localized cancer may be treated with surgery, but a cancer that has metastasized is difficult to surgically remove. For more specific information on treatment see entries for 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 disease, non-Hodgkin's lymphoma, multiple myeloma and hepatic angiosarcoma.Risk: Risk factors for cancer include, among others, 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; infection with certain viruses (e.g., hepatitis B and C, Epstein-Barr virus, human immunodeficiency virus [HIV]) or other biological agent (e.g., Schistosoma, Helicobacter pylori); radiation exposure (either environmental or high-dose therapeutic); anti-cancer (cytotoxic) drugs treatment; occupational or environmental carcinogen exposure, such as to asbestos, heavy metals, pesticides, hair dressing compounds, soot, tar, formaldehyde, vinyl chloride, and wood dusts; and advanced age. In women, risk factors include certain reproductive and sexual factors such as early age at first menstruation (menarche), late age at menopause, never having been pregnant (nulliparity), not carrying a pregnancy beyond 6 months, late first pregnancy (35 years or older), and having multiple sexual partners, as well as infection with certain viruses (e.g., human papillomavirus), hormone therapy (e.g., estrogen, androgenic steroids), and low socioeconomic status. Gender may predispose some individuals to certain types of cancer. A genetic predisposition for certain cancers may occur within family groups. Blacks are at highest risk for new cancers; cancer risk is low in Native Americans and Alaska Natives (“Cancer Trends Report”). Incidence and Prevalence: Cancer incidence is estimated to be 468.1 new cancers diagnosed per 100,000 Americans annually, including prostate cancer 155.4 per 100,000; breast cancer 125.5 per 100,000; colon cancer 47.4 per 100,000; and lung cancer 62.9 per 100,000 (SEER). Types of cancer with rising incidence include female lung cancer, non-Hodgkin lymphoma, and skin cancer (melanoma) (“Cancer Trends Report”). Cancer is second only to heart disease as the leading cause of death in the US.
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