Cancer is the name given to a collection of related diseases and there are more than 200 clinically recognised types, although every cancer is unique. In all types, some of the body’s cells begin to divide without stopping and spread into surrounding tissues. According to Cancer Research UK 1 in 2 people in the UK will get cancer in their lifetime.
Cancer can start almost anywhere in the human body, which is made up of trillions of cells. Normally, human cells grow and divide to form new cells as the body needs them. When cells grow old or become damaged, they die, and new cells take their place.
When cancer develops, however, this orderly process breaks down. As cells become more and more abnormal, old or damaged cells survive when they should die, and new cells form when they are not needed. These extra cells can divide without stopping and may form growths called tumours. Many cancers form solid tumours, but cancers of the blood, such as leukemias, generally do not form solid tumours.
Cancerous tumours are malignant, which means they can spread into, or invade, nearby tissues. In addition, as these tumours grow, some cancer cells can break off and travel to distant places in the body through the blood or the lymph system and form new tumours far from the original tumour.
When a tumour successfully spreads to other parts of the body and grows, invading and destroying other healthy tissues, it is said to have metastasised. This process itself is called metastasis, and the result is a serious condition that is very difficult to treat.
Unlike malignant tumours, benign tumours do not spread into, or invade, nearby tissues. Benign tumours can sometimes be quite large, however. When removed, they usually don’t grow back, whereas malignant tumours sometimes do. Unlike most benign tumours elsewhere in the body, benign brain tumours can be life threatening.