How do tumours develop?

Our bodies are made up of many types of cells, all of which are specialised depending on where they are located.  For example, there are bone cells in bone and nerve cells in the brain. Most liver tissue is made up of liver cells (hepatocytes).

Normally, all of our cells grow and multiply in a controlled manner that produces more cells as they are needed to keep the body healthy. When cells become old or damaged, they die and are replaced with new cells.

Sometimes, however, this orderly process of cell growth and division goes wrong.

The genetic material (DNA) of a cell can become damaged or changed by disease, the environment or genetic factors that produce alterations (called mutations), which affect normal cell growth and division. When this happens, old cells do not die when they should and new cells may form when the body does not need them. These unneeded cells can group together in a mass of tissue that is called a tumour.  Some tumours are “benign” (not harmful to the body).  Tumours that are harmful (“malignant”) cause cancer. The term "cancer" applies to many diseases that occur when the cells of the body multiply in an uncontrolled manner, grow into solid tissue lumps and invade healthy tissues.

The organ where a cancer originated is called the "primary cancer site" and this site gives cancer its name, like “liver cancer” or “colorectal cancer”.

Cancer that has spread from the primary site to another organ (e.g. the liver or lungs) is called metastatic or secondary cancer.

Once cancerous tumours begin to attack vital parts of the body, such as airways, the brain, the kidney or the liver, they can affect the way that organ normally functions and can cause death.