Cancer: what is it?
What is cancer?
Throughout our lives, healthy cells in our bodies divide and replace themselves in a controlled sequence. Sometimes, however, a cell begins to reproduce abnormally for no apparent reason. These abnormally dividing cells may spread to other parts of the body and begin reproducing there. The spread of these cancerous cells is a process called metastasis. Eventually this abnormal tissue interferes with the ability of the body and its cells, organs and other structures to perform their normal function, and illness or death may result.
The term 'cancer' is actually applied to more than 100 diseases that affect nearly every part of the body. All can be potentially life-threatening. They all have different causes, cause different symptoms, and vary in aggressiveness (the speed at which they spread). However, most types of cancer fall into 4 main categories.
- Carcinomas — these are the most commonly diagnosed cancers that affect the skin, mucous membranes, lungs, breasts, pancreas and other organs and glands.
- Leukaemias — these are cancers of the blood and blood-forming tissues and do not form solid tumours.
- Sarcomas — these are cancers that affect the bones, muscle and connective tissue and include many of the rarer forms of cancer.
- Lymphomas — these are cancers that affect the lymphatic system (a network of vessels that is an important part of the body's immune system).
Tumour formation
A tumour or lump is a cluster of abnormally dividing cells. Most, but not all, cancers form tumours. Malignant or cancerous tumours crowd out the healthy cells in the body, interfere with body functions, draw nutrients from body tissues and form new tumours in other parts of the body.
What causes cancer?
At present it is not known exactly what triggers some cells to become cancerous. For a healthy cell to turn malignant, its genetic code must be changed or reprogrammed for constant, uncontrolled cell division. Substances that either start or promote the process are called carcinogens, and there are many types.
Environmental factors
Environmental factors, as well as diet, are now thought to be among the major causes of cancer. For example, people exposed to cigarette smoke have significantly higher rates of lung cancer than other people. Smoking is also linked to cancer of the head and neck areas, bladder, kidney, stomach, cervix and pancreas, as well as some leukaemias. Another environmental factor is overexposure to sunlight, causing several types of skin cancers, including melanoma.
Many substances in the environment have been identified as carcinogens but, generally, high levels or long-term exposure to these are needed to cause cancer. These types of environmental carcinogens include various chemicals, gases and other substances found in the air, water and food.
Diet and nutrition
A diet that is high in fat and low in fibre is associated with a greater risk of colorectal cancer and is now considered a factor in several other cancers. Other dietary habits associated with cancer include over-consumption of alcohol, fat and foods that have been smoked, cured, pickled or charred.
Age and genetics
The risk for most cancers increases with age. Inherited, or familial, predisposition is also considered a risk factor, although the influence will vary from case to case.
All these factors may contribute to cancer; however, cancer is not actually caused by one single factor. Cancer most commonly is caused by multiple factors including age, inherited predisposition, general health and exposure to carcinogens. As such, everyone’s cancer risk profile is complex and unique.
Last Reviewed: 06 November 2009
- 1. National Cancer Institute. US National Institutes of Health. What is cancer? [Website]. Updated July 2010. http://www.cancer.gov/cancertopics/what-is-cancer/print?page=&keyword= (accessed July 2010).
2. American Cancer Society. What is cancer? [Website]. http://www.cancer.org/Cancer/CancerBasics/what-is-cancer (accessed July 2010).
3. Cancer Council NSW. What is cancer? [Website]. http://www.cancercouncil.com.au/editorial.asp?pageid=2169#whatis (accessed July 2010).
