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What Is Cancer? | Genetics | Biology | FuseSchool

What happens to cells for cancerous growths to occur? Your body is made up of millions and millions of cells. In fact there are between 50 and 75 trillion cells in the body.

These cells are dying and being replaced all the time. Cancer can start when just one of the trillions of cells begins to grow and multiply too much. The result is a mass of cells called a tumour. The starting place of abnormal cell growth and division is called the primary tumour, and they can start almost anywhere in the human body.

Changes take place within the genes of a cell or group of cells, resulting in the abnormal cell division. Genes are specific codes of DNA that tell the cell what to do by coding for specific proteins or an RNA molecule. Proteins and RNA together control the cell. They decide what type of cell it is, what it does, when it divides and when the cell will die. When cells divide by mitosis, the DNA is replicated and sometimes mistakes are made. These are called mutations.

Lots of mutations are silent; they have no effect on the cell because they occur in non-coding regions of the DNA. But sometimes, mutations in certain genes may mean that too many proteins are produced that trigger a cell to divide. Or proteins that normally tell a cell to stop dividing may not be produced. The cells starts to grow out of control. There have to be at least about 6 or more mutations to coding DNA before a normal cell turns into a cancer cell.

Cells are usually very good at repairing damage to genes; they have special repair mechanisms in place. But over time, the damage may build up. And then it can be a domino effect; once the cells start growing too fast and dividing rapidly, they are more likely to pick up even more mutations and less likely to repair the damage.

So mutations do the damage, but what causes them to happen? Whilst mutations can happen by natural processes, they can also be triggered by lifestyle. For example, there are cancer-causing substances, known as carcinogens, in tobacco smoke. In fact, more than 4 out of 5 cases of lung cancer are caused by smoking. Genetics also have a role to play; faulty genes can be passed from parent to offspring. Most inherited cases of breast cancer are associated with two abnormal genes: BRCA1 and BRCA2. Other cancer-causing factors include exposure to radiation, exposure to UV radiation from the sun and some chemicals in the environment amongst other things.

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