Cancer is not one disease but many. They behave in different ways, respond differently to treatment and may have many different causes.
A cancer cell differs from a normal body cell in that it appears to have undergone a mutation or change in its genetic material. It seems to be not only different but also to have escaped the normal controlling forces which govern all body cells.
Cancer cells go on reproducing and so the cancer enlarges. They also tend to spread beyond the original tissue. They may spread locally or may travel to distant parts of the body through the lymph channels or through the veins.
What triggers off the mutation or change in a normal cell making it into a cancer is unknown. Some believe that these mutations are happening all the time, but the body normally mounts a good defence and destroys “rogue” cells and so a cancer doesn’t develop. It may be that there is a change in the body’s defences which allows the cancer cells to escape this normal control.
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