What is it?

How does cancer develop?

Put simply, your body is made up of millions of tiny building blocks. These are called cells.

For our bodies to grow and function normally, old cells must be replaced by new ones. Normally this process of producing and replacing cells happens in a controlled way, but sometimes it goes out of control, producing abnormal, cancerous cells that keep on dividing in an uncontrolled way. They can then crowd out healthy cells, and may spread to other parts of the body.

There are two main types of cancer:

Solid cancers: These form when abnormal cells crowd out healthy cells, forming a lump, or tumour. This characterises many types of cancer. Some tumours are benign, meaning they are harmless, and often do not need treatment. But malignant tumours - the cancers - can spread and need to be treated.

Leukaemias and lymphomas: These occur when cells divide and multiply abnormally, but they do not form tumours. Sometimes leukaemia is only diagnosed after a routine blood test.

What is cancer and how does it develop? Watch our Flash movie to find out.