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Cancer cells are cells that grow and divide at an unregulated, quick pace. Although cancer cells can be quite common in a person, they are only malignant when the other cells (particularly natural killer cells) fail to recognize and/or destroy them. In the past a common belief was that cancer cells failed to be recognized and destroyed because of a weakness in the immune system. However more recent research has shown that the failure to recognize cancer cells is caused by the lack of particular co-stimulated molecules that aid in the way antigens react with lymphocytes.〔(Creating Cancer Killers ). Research.uky.edu. Retrieved on 2010-12-01.〕 ==Causes== By researching stem cells scientists have suggested that too much SP2 protein may turn stem cells into cancer cells.〔(Too much SP2 protein turns stem cells into 'evil twin' cancer cells ). Sciencedaily.com (2010-10-27). Retrieved on 2010-12-01.〕 Other issues thought to play a role in the spread of cancer include viruses, immune system issues, genetics, environment and age.〔(What causes cancer? : Cancer Research UK : CancerHelp UK ). Cancerhelp.org.uk (2010-07-15). Retrieved on 2010-12-01.〕 However, a lack of particular co-stimulated molecules that aid in the way antigens react with lymphocytes can impair the natural killer cells ability and ultimately cause cancer.〔 All cancers begin in cells, the body's basic unit of life. To understand cancer, it's helpful to know what happens when normal cells become cancer cells. The body is made up of many types of cells. These cells grow and are controlled to produce more cells as they are needed to keep the body healthy. When cells become old or damaged, they die and are replaced with new cells. Sometimes this process of controlled production of cells goes wrong. The genetic material (DNA) of a cell start producing mutations that affect normal cell growth and division by being damaged. When this happens, sometimes these cells do not die but form a mass of tissue called a tumor. Said mutations accumulate, being another reason that cancer is found more often in older people. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Cancer cell」の詳細全文を読む スポンサード リンク
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