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Cancer is, ultimately, a disease of genes. Typically, a series of several mutations is required before a cell becomes a cancer cell. We distinguish between oncogenes, which promote cancer when "switched on" by a mutation, and tumor suppressor genes, which prevent cancer unless "switched off" by a mutation. These mutations can have various causes: radiation or chemicals called carcinogens; some inherited predisposition is not uncommon; some viruses that can cause cancer have also been described. Usually, they carry in their genome some oncogene or tumor suppressor inactivating gene. In about 15% of all cancers, viruses seem to play a role; Bacteria, like Helicobacter pylori, also induce carcinogenesis by a process of chronic inflammation. Finally, damage by free radicals, which are a natural by-product of oxygen metabolism, can cause mutations in the DNA.
A cell that degenerates into a tumor cell does usually not acquire all these properties at once, but its daughter cells are selected to build them. This process is called cellular evolution. A first step in the development of a tumor cell is usually a small change in the DNA, often a point mutation, which leads, among other things, to a genetic instability of the cell. The instability increases to a point where the cell loses whole chromosomes, or has double ones. Also, the DNA methylation pattern of the cell changes, activating and deactivating genes more or less at random. Cells that divide at a high rate, such as stem cells, show a higher risk of becoming tumor cells than those which divide less or not at all, for example neurons. If the initial tumor cell (or group of tumor cells) is not removed by the immune system, it will develop into cancer.
Carcinogenesis (lit.: creation of cancer) is the process of derangement of the rate of cell division.
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- Cancer Consultants.com
Provides information on treatment and prevention for patients and professionals. - CancerExperts MD
Physcians located in Boston offer second opinions and personalized case reviews. Provides an online ask-a-doctor service. - Meds.com: Cancer Glossary
Aims to provide a better understanding of words frequently used in patient care. - Cancer Rates And Risks
Provides international incidence and mortality rates including information about risk factors. From the U.S. National Cancer Institute. - WebMD Health: Cancer
Consumer health site which includes information for the newly diagnosed, as well as for those coping with chemotherapy.