Tumor

See the article about cancer for the main article about malignant tumors.

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Tumor (American English) or tumour (British English) originally means "swelling", and is sometimes still used with that meaning. Tumor meaning swelling is one of the five classical characteristics of inflammation. However, the term is now primarily used to denote abnormal growth of tissue. This growth can be either malignant or benign.

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Malignant tumors are called cancer. Cancer has the potential to invade and destroy neighboring tissues and create metastases. Benign tumors do not invade neighboring tissues and do not seed metastases, but may locally grow to great size. They usually do not return after surgical removal.

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Depending on tissue of origin, tumors may be:

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• Tumors of epithelial origin.
• squamous epithelium: squamous cell papilloma, squamous cell carcinoma
• transitional epithelium: transitional cell papilloma, transitional cell carcinoma
• basal cell (only in skin): basal cell carcinoma
• glandular epithelium: adenoma, cystadenoma, adenocarcinoma
• tubules epithelium (kidney): renal tubular adenoma, renal cell carcinoma (Grawitz tumor)
• hepatocytes: hepatocellular adenoma, hepatocellular carcinoma
• bile ducts epithelium: cholangiocellular adenoma, cholangiocellular carcinoma
• melanocytes: melanocytic nevus, malignant melanoma
• Tumors of mesenchymal origin:
• connective tissue:
• fibroma, fibrosarcoma
• myxoma, myxosarcoma
• chondroma, chondrosarcoma
• osteoma, osteosarcoma (osteogenic sarcoma)
• lipoma, liposarcoma
• muscle:
• leiomyoma, leiomyosarcoma
• rhabdomyoma, rhabdomyosarcoma
• endothelium:
• hemangioma (capillary h., cavernous h.), glomus tumor, hemangiosarcoma, Kaposi sarcoma
• lymphangioma, lymphangiosarcoma
• Tumors of blood cells:
• hematopoietic cells: leukemia
• lymphoid cells: non-Hodgkin lymphoma, Hodgkin lymphoma
• Tumors of germ cells:
• Teratoma (mature teratoma, immature teratoma)

An epithelial tumor is considered malignant if it penetrates the basal lamina and is considered benign if it does not.

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Tumors are caused by mutations in DNA of cells. An accumulation of mutations is needed for a tumor to emerge. Mutations that activate oncogenes or repress tumor supressor genes can eventually lead to tumors. Cells have mechanisms that repair DNA and other mechanisms that cause the cell to destroy itself by apoptosis if DNA damage gets too severe. Mutations that repress the genes for these mechanisms can also eventually lead to cancer. A mutation in one oncogen or one tumor repressor gen is usually not enough for a tumor to occur. A combination of a number of mutations is necessary.

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DNA microarrays can be used to determine if oncogenes or tumor repressor genes have been mutated. Possibly in the future tumors can be treated better by using DNA microarrays to determine the exact characteristics of the tumor.

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As people get older, they accumulate more mutations in their DNA. This means that the prevalence of tumors increases strongly with increasing age. It is also the case that the older a person with a tumor is, the higher the chances are that the tumor is malignant. For example, if a woman of 20 years old has a tumor in her breast it is very likely that the tumor is benign. However, if a woman of 70 has a tumor in her breast it is almost certain that it is malignant.

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Tumor: See also ►



 

American English: American English (AmE) is the form of the English language used mostly in the United States of America. It is the primary language used in the United States. As of 2005, more than two-thirds of native speakers of English use various forms of American English. American English is also sometimes calle...

British English: British English (BrE) is a term used loosely to refer to the form of the English language written in the British Isles, and more narrowly as spoken in the south of England (extending elsewhere with varying degrees). For historical reasons dating back to the rise of London in the 9th century, the var...

Inflammation: Inflammation is the first response of the immune system to infection or irritation and may be referred to as the innate cascade. Inflammation is characterized by the following quintet: redness (rubor), heat (calor), swelling (tumor), pain (dolor) and dysfunction of the organs involved (functio laes...