What is cancer?

Q: What is cancer?
A: The body is made up of trillions of living cells. Normal body cells grow, divide to make new cells, and die in an orderly way. During the early years of a person셲 life, normal cells divide faster to allow the person to grow. After the person becomes an adult, most cells divide only to replace worn-out or dying cells or to repair injuries.
Cancer begins when cells in a part of the body start to grow out of control. There are many kinds of cancer, but they all start because of out-of-control growth of abnormal cells.
Cancer cell growth is different from normal cell growth. Instead of dying, cancer cells
continue to grow and form new, abnormal cells. In most cases the cancer cells form a
tumor. Cancer cells can also invade (grow into) other tissues, something that normal cells
cannot do. Growing out of control and invading other tissues are what makes a cell a
cancer cell.
Cells become cancer cells because of damage to DNA. DNA is in every cell and directs all its actions. In a normal cell, when DNA is damaged the cell either repairs the damage or the cell dies. In cancer cells, the damaged DNA is not repaired, but the cell doesn셳 die like it should. Instead, this cell goes on making new cells that the body doesn셳 need.
These new cells will all have the same damaged DNA as the first abnormal cell does. People can inherit damaged DNA, but most often the DNA damage is caused by mistakes that happen while the normal cell is reproducing or by something in our environment. Sometimes the cause of the DNA damage is something obvious, like cigarette smoking. But often no clear cause is found.
Cancer cells often travel to other parts of the body, where they begin to grow and form
new tumors that replace normal tissue. This process is called metastasis. It happens when
the cancer cells get into the bloodstream or lymph vessels of our body.
Reference : www.cancer.org

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