What is Cancer?

Cancer is a disease of the body’s cells, which are the body’s basic building blocks. Our bodies constantly make new cells: to enable us to grow, replace worn-out cells, or to heal damaged cells after an injury. Certain genes control this process.

All cancers are caused by damage to these genes. The reason for this damage is unknown. It usually happens during our life, although a small number of people inherit a damaged gene from a parent. Normally, cells grow and multiply in an orderly way. However, over time damaged genes can cause them to behave cells to behave abnormally. Changes in genes over a period of time may grow into a lump called a tumour.

Tumours can be benign (not cancer) or malignant (cancer). Benign tumours do not spread outside their normal boundary to other parts of the body.

The beginnings of cancer   Normal cells Abnormal cells Abnormal cells multiply Malignant or invasive cancer Boundary Lymph vessel Blood vessel Some benign tumours are precancerous and may progress to cancer if left untreated. Other benign tumours do not develop into cancer.

A malignant tumour is made up of cells. When it first develops, this malignant tumour may be confined to its original site. This is known as a cancer in-situ (or carcinoma in-situ). If these cells are not treated, they may spread beyond their normal boundaries and into surrounding tissues, becoming invasive cancer.

For a cancer to grow bigger than the head of a pin, it must grow its own blood vessels. This is called angiogenesis. Sometimes cells move away from the original (primary) cancer, either by the local tissue channels (lymphatics) or in the blood stream, and invade other organs. When these cells reach a new site, they may continue to grow and form another tumour at that site. This is called a secondary cancer or metastasis.

How cancer spreads

Click on diagram for larger view

© 2008 Cancer Council