The human body is made up of billions of cells that group together to form organs and tissue such as the skin, bones, muscles, lungs and kidneys.
Typically, cells grow and over time they die and are replaced by new cells. Cancer occurs when abnormal cells begin to multiply and divide without stopping and spread into surrounding tissues or other parts of the body.
When these groups of abnormal cells form lumps or growths, they are called tumours. They behave differently depending on whether they are cancerous (malignant), non-cancerous (benign) or pre-cancerous.