Cancer is a disease of the cells, which are the body’s basic building blocks. Cancer starts in our genes. Our bodies constantly make new cells to enable us to grow, to 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. This damage usually happens during our lifetime, although a small number of people inherit a damaged gene from a parent. Normally, cells grow and multiply in an orderly way. However, damaged genes can cause them to behave abnormally. They may grow into a lump called a tumour.
Tumours can be benign (not cancer) or malignant (cancer).
Benign tumours (not cancer)
Benign tumours do not spread outside their normal boundary to other parts of the body. Some benign tumours are precancerous and may progress to cancer if left untreated. Other benign tumours do not develop into cancer. However, if a benign tumour continues to grow at the original site, it can cause a problem by pressing on nearby organs.
Malignant tumours (cancer)
A malignant tumour is made up of cancer 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.
How cancer spreads
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 fluid channels (lymphatics) or in the bloodstream, 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.
What causes cancer?
The causes of many cancers are not yet known. Many cancers seem to be associated with our lifestyle habits and recreation, or by substances in our environment that affect our bodies. However, doctors often cannot explain why one person develops cancer and another does not.
Things that increase the risk of cancer include:
- sun exposure
Cancer causing substances are called carcinogens. Cancer is not catching. It cannot be passed on to friends or relatives or anyone else like a cold or the flu. People who have a family history of some cancers, such as breast and bowel cancer, may have a higher risk of developing that cancer. In a very small number of families a change in the gene that controls cell growth is passed on from one generation to the next. Not all family members get this change. Those individuals who do may have a higher than usual chance of developing cancer.