How does cancer develop
Cancer develops when cells in a part of the body begin to grow out of control. Although there are many kinds of cancer, they all start because of uncontrolled growth of abnormal cells. The body is made up of many types of cells. These cells grow and divide in a controlled way 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.
Proteins are the building blocks that make up a cell. Some proteins act as ‘on/off’ switches that help to control how a cell behaves. For example, a hormone signal acts on a protein in or on the cell. The protein then sends a signal down a chain of switches. The final signal tells the cell to reproduce by dividing into two. Genes are coded messages inside a cell that tell it how to behave. The genes are codes that tell the cell how to make many different proteins. One gene ‘codes’ for one protein. Mutations can happen by chance when a cell is reproducing. It is not easy for a normal cell to turn into a cancer cell. There have to be about half a dozen different mutations before this happens. Cells often self destruct if they carry a mutation. Or they might be recognised by the immune system as abnormal and killed. This means most pre-cancerous cells die before they can cause disease. Only a few turn into a cancer.
However, sometimes this orderly process goes wrong. The genetic material (DNA) of a cell can become damaged or changed, producing mutations that affect normal cell growth and division. When this happens, cells do not die when they should and new cells form when the body does not need them. The extra cells may form a mass of tissue called a tumor. Most of the time when DNA becomes damaged, either the cell dies or is able to repair the DNA. In cancer cells, the damaged DNA is not repaired. People can inherit damaged DNA, which accounts for inherited cancers. Many times though, a person’s DNA gets damaged by things in the environment, like,chemicals, viruses, tobacco smoke or too much sunlight. This causes changes to the normal cell behaviour, for example, a signalling protein may be permanently switched on. Other proteins, whose job is to control and limit cell division, may be permanently switched off.
Because cancer cells keep growing and dividing, they are different from normal cells. Instead of dying, they outlive normal cells and continue to grow and make new abnormal cells. Cancer usually forms as a tumor (a lump or mass.) Some cancers, like leukemia, do not form tumors. Instead, these cancer cells involve the blood and blood-forming organs, and circulate through other tissues where they grow. Cancer cells often travel through the bloodstream or through the lymph system to other parts of the body where they begin to grow and replace normal tissue. This spreading process is called metastasis.
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