What is cancer?

Our bodies are made up of billions of tiny parts that fit together like building blocks. These parts are called cells.

Normally, healthy cells grow, divide and, in time, get worn out and die. This usually happens in an orderly and controlled way without any problems. If something goes wrong this process gets out of control, so the cells carry on dividing and don’t die in the normal way. Often, these cells form a lump called a tumour.

Tumours can be benign (non-cancerous) or malignant (cancerous). Doctors can tell whether a tumour is cancerous or not by looking at a small sample of cells under a microscope.

• In a benign tumour, the cells do not spread to other parts of the body and so are not cancerous. They can cause problems if they carry on growing at the original site and press on surrounding organs.
• In a malignant tumour, the cancer cells can spread beyond the original area of the body. If a tumour is not treated, it may spread into surrounding tissue.

Sometimes, cells break away from the original (primary) tumour and spread to other parts of the body. When the cancer cells reach a new area, they may carry on dividing and form a new tumour. This is known as a secondary cancer or a metastasis. This is why having treatment as soon as possible is important.

A tumour can form inside:

• an organ (part of the body that does a specific job, such as the liver or kidney). These are sometimes called solid tumours.
• a bone
• the lymphatic system (a network that helps defend your body from disease). This is called a lymphoma.

Cancer can also occur in the blood cells in the bone marrow (the spongy centre of your bones where your blood cells are made). This type of cancer is called leukaemia.