Illustration of a pear on top of a pile of books

Home Class activities Facts about cancer Real life experiences Support Getting involved
HOME > Facts about cancer > What is cancer?	Search

What is cancer?

Cancer is not a single disease with a single cause or type of treatment. There are more than 200 types of cancer, each with its own name, behaviour and treatment. Cancer can occur in any organ of the body and everyone’s experience is unique and personal.

Cells and genes

The organs and tissues of the body are made up of cells. Each cell has a nucleus, or control centre, containing coded instructions called genes. The genes tell the cell what type of cell it should be, e.g. skin, bone or blood. The genes also tell the cells when to divide and replicate themselves in an orderly and controlled manner and how to repair damage done through everyday living.

All kinds of cancer, including childhood cancer, develop when the genes that normally keep our cells healthy develop a fault.

Genes act as control mechanisms to stop cells dividing too much. However, in abnormal or faulty cells the control mechanisms do not work, and the cell divides uncontrollably, developing into a lump or cluster of cells which is called a tumour.

Tumours

Some tumours are benign or harmless because they do not invade the surrounding tissues or spread to other parts of the body. Therefore they are not cancerous, and may not need treatment. But malignant tumours – the cancers – have the ability to spread (metastasize) beyond the original site to other organs and tissues via the bloodstream or lymphatic system, and require treatment. These cells may continue reproducing in the new site forming a new tumour. For example, a woman originally diagnosed with breast cancer may later develop a secondary cancer in her lungs.

Your pupils or students may be interested in the animated ‘What is cancer?’ movie on our website for young people.

Causes of cancer

What causes cancer in an individual varies from cancer to cancer, and from person to person. The most common causes of cancer are environmental factors such as smoking, sun damage, diet or viruses. A less common cause is genetic factors, when genetic faults are inherited from our relatives.

The other pages in this section provide more detail on the main cancers that occur in children and young people.