Cell changes and cancer
All cancers begin in cells. Our bodies are made up of more than a hundred million million (100,000,000,000,000) cells. Cancer starts with changes in one cell or a small group of cells.
Usually we have just the right number of each type of cell. This is because cells produce signals to control how much and how often the cells divide. If any of these signals are faulty or missing, cells may start to grow and multiply too much and form a lump called a tumour. Where the cancer starts is called the primary tumour.
Some types of cancer, called leukaemia, start from blood cells. They don’t form solid tumours. Instead, the cancer cells build up in the blood and sometimes the bone marrow.
For a cancer to start, certain changes take place within the genes of a cell or a group of cells.
Genes and cell division
Different types of cells in the body do different jobs, but they are basically similar. They all have a control centre called a nucleus. Inside the nucleus are chromosomes made up of long strings of DNA (deoxyribonucleic acid). DNA contains thousands of genes, which are coded messages that tell the cell how to behave.
Where genes are in cells
Each gene is an instruction that tells the cell to make something. This could be a protein, or a different type of molecule called RNA. Together, proteins and RNA control the cell. They decide what sort of cell it will be, what it does, when it will divide, and when it will die.
Gene changes within cells (mutations)
Normally genes make sure that cells grow and reproduce in an orderly and controlled way. They make sure that more cells are produced as they are needed to keep the body healthy.
Sometimes a change happens in the genes when a cell divides. The change is called a mutation. It means that a gene has been damaged or lost or copied twice. Mutations can happen by chance when a cell is dividing. Some mutations mean that the cell no longer understands its instructions and starts to grow out of control. There have to be about half a dozen different mutations before a normal cell turns into a cancer cell.
Mutations in particular 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. Abnormal proteins may be produced that work differently to normal.