Cancer occurs when normal body cells get out of control, multiply and spread. These cells clump together to form a cancerous or malignant tumour which can then grow and damage healthy parts of the body.

There are several different types of NET. The most common one is called a carcinoid tumour. NETs usually start in the bowel, but they can grow in other parts of the body too, such as the pancreas and lungs.

NETs share some common features. They tend to grow very slowly, for instance, and they often produce chemicals or hormones that travel around the body in the bloodstream and cause symptoms such as hot flushes and diarrhoea.