The immune system attacks and eliminates not only bacteria and other foreign substances but also cancer cells. A cancer cell is a cell not strange, it is a cell whose biological function has been altered so that does not meet the body’s normal mechanisms that control the growth and reproduction of it. The abnormal cells can continue to grow, turning into cancer.
In the immune system, a large part of the body’s defense against cancer is carried out directly by cells, rather than by antibodies circulating in the blood. For example, the presence of tumor antigens on cancer cells can activate certain white blood cells (lymphocytes and in a much lesser degree, monocytes) which perform an immune surveillance seeking and destroying cancer cells.
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A multitude of factors, genetic and environmental, increase the risk of developing cancer.
Cancer cells develop from normal cells in a complex process called transformation. The first step is the initiation process in which a change in the cell’s genetic material prepares to become cancerous. This change is caused by an agent called a carcinogen (may be a chemical, a virus, radiation, or sunlight). However, not all cells are equally susceptible to carcinogens. A genetic defect in the cell or other agent, known as a promoter, including 
Treatments
Mainly, there are three types of 
