The human body is made up of billions of cells, which in a healthy body are usually turning over slowly, in an organised way. Cancer is the term we use for a disease that occurs when these cells grow in an abnormal and uncontrolled way. This uncontrolled growth of cells can cause a lump or a mass to form, which is called a tumour. Tumours can be benign or malignant.
Benign tumours usually grow slowly and do not spread to other parts of the body. Benign tumours only become a problem if they grow very large, taking up space and affecting the way the body works. Malignant tumours are made up of cancer cells. They are usually faster growing, can destroy tissue and have the ability to spread to other parts of the body.
Cancer may also affect blood cells, causing blood cancers such as leukaemia, lymphoma or myeloma. These blood cancers also cause normal blood cell production to be reduced due to the uncontrolled growth of the abnormal (malignant) cells in the bone marrow.
Over time, the uncontrolled growth of cancer cells usually becomes too much for the body to cope with, or will spread to a part of the body that is essential for life.