About cancer

Your body is made up of millions of cells. There are about 200 different types, each with its own unique structure and function. For example, a muscle cell is very different from a brain cell, and so on. Cancer is a disease of the cells.

Cancer cells

Throughout your life, your cells continue to divide and make copies of themselves. These new cells help you grow or they replace older cells. However, if something goes wrong when the cells are dividing, an abnormal cell may be produced. When this happens, the cell usually destroys itself.

But, sometimes, abnormal cells continue to divide, producing more abnormal cells. In some cases, they divide and grow faster than normal cells. Cancer is the name given to an abnormal growth of malignant cells. ‘Malignant’ means that the abnormal cells have the potential to spread to other parts of the body if they are not treated. You may also hear the word ‘malignant’ being used to mean cancer.

Types of cancer

Solid cancers or tumours

This is when a lump forms because the cells in a particular part of your body, such as your bones, muscles, brain or a lymph node, have divided and multiplied abnormally.

Not all tumours are cancerous. If you have been diagnosed with a ‘benign’ tumour, this means it is not cancer. A benign tumour doesn’t have the ability to spread to other parts of your body and it will only start causing problems if it grows too large and interferes with how your body works.

However, malignant tumours do have the ability to spread through cells breaking away from the lump and beginning to grow in another part of the body. They are classified by how far they have spread (their stage) and how abnormal they look under the microscope (their grade).


Leukaemias occur when the blood cells divide and multiply abnormally. The most common types of leukaemia in young people, acute lymphoblastic leukaemia (ALL) and acute myeloid leukaemia (AML), are named after the white blood cells that are affected by the cancer.

Other types and more information

For more information about particular cancers, see our types of cancer section. You can also download or order our booklet Cancer and treatment free of charge.

Updated December 2014, next review due 2017.