How does cancer begin?
Your body is made up of 100 million million cells. Cancer can start when just one of them begins to grow and multiply too much. The result is a growth called a tumour. Benign tumours are localised growths - they only cause problems if they put pressure on nearby tissues, such as the brain. Much more serious are malignant tumours, which invade the surrounding body tissues. Some malignant tumours also spread throughout the body via the bloodstream: a process called metastasis.