About cancer

The body is made up of millions of cells. There are about 200 different types which all do different jobs, have different shapes and behave in different ways. A muscle cell is different to a bone cell, which is different to a skin cell and so on.

Throughout your child's life, cells continue to divide and make copies of themselves. These new cells help them 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.

Cancer cells

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.

Solid cancers or tumours

This is when a lump forms because the cells in a particular part of the body, such as the bones, muscles, brain or lymph nodes, have divided and multiplied abnormally. Not all tumours are cancerous. If your child has 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 their body and it will only start causing problems if it grows too large and interferes with how their body works.

However, malignant tumours do have the ability to spread through the body. The abnormal cells can break away from the lump and begin to grow in another part of the body. The cancer is usually classified by how far the cells 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.


Lymphomas occur when the cells of the lymphatic system divide or multiply abnormally. This can produce large lumps in the lymph glands, which are located in the neck, groin, under the armpit and throughout the body.

For more information about particular cancers, see our types of cancer section.

Updated September 2017, next review due 2019.