Cancer
Plain language: background
Information has been provided here on a plain language summary of what is known about cancer.
Plain language
- » What is known about cancer?
- What is cancer?
- How do cancers happen?
- How does cancer spread?
- What are ‘risk factors’ for cancer?
- How is cancer diagnosed?
- References
What is known about cancer?
What is cancer?
‘Cancer’ is characterised by an overgrowth of cells that serves no useful purpose and is not under the normal control of cell growth and specialisation [1-3].
Cancer is not a single disease, but a large number of diseases. Many types of cancer can spread throughout a person’s body.
Cancers are sometimes called ‘tumours’ and ‘neoplasms’, but these terms can also be used for non-cancerous growths.
Neoplasms can be ‘benign’ (not cancerous) or ‘malignant’ (cancerous).
Generally, a cancer:
- is made up of relatively unspecialised cells;
- grows quickly and invades surrounding tissues; and
- can lead to secondary areas of tumour growth in other areas of the body (a process known as metastasis).
The place where the cancer first develops (such as in the lungs) is known as the ‘primary’ site, and where it occurs as a result of metastasis (such as bones for lung cancer) as a ‘secondary’ site.
How do cancers happen?
For all cancers, there are changes (mutation) of particular genes within a cell (there are four main types of genes that control cell growth) [2, 3].
This alteration damages the mechanisms that regulate normal cell growth and differentiation.
Mutations that make a person more likely to develop cancer may be inherited [2, 3].
They can also occur by themselves or after exposure to something in the environment (such as chemicals – as in tobacco smoke – radiation or some viruses).
As well, changes to a person’s immune system may reduce the body’s ability to recognise and destroy abnormally mutated cells. (This can happen, for example, when a person has HIV/AIDS.)
How does cancer spread?
After development of a primary cancer (such as cancer of the lung or breast), it can spread in three main ways:
- spreading into body cavities or surfaces;
- through the body’s lymphatic system; (The lymphatic system is made up mainly of very thin tubes running throughout the body. These tubes collect fluid that leaks from the very small blood vessels (capillaries) and returns it to the blood circulation through a special channel called the thoracic duct.)
- penetration of blood vessels and spread with blood [2, 3].
The process of cancer spread is known as metastasis [2, 3]. A tumour/neoplasm with the ability to metastasise is, by definition, malignant.
What are ‘risk factors’ for cancer?
Different kinds of cancer have different risk factors – that is, factors that are linked with their development – but a number of cancers share common risk factors [2-4]. (It is important to know that some people with one or more risk factors may never develop a cancer, and that other people who do develop cancer have no apparent risk factors. Even when a person who has a risk factor is diagnosed with cancer, there is no way to prove that the risk factor actually caused the cancer.)
Environmental factors are believed to be associated with around three-quarters of all cancers [1]. These include:
- chemicals
- diet
- infectious diseases
- radiation
Some cancers may be a result of inherited genetic faults, which can also play a part in the development of cancers more linked with environmental factors. The causes are unknown for many cancers.
Important risk factors for cancer are tobacco use (through inhaled chemicals), unhealthy diet, and lack of physical activity [1]. It is believed that about one-third of all cancer deaths are related to dietary factors and lack of physical activity in adulthood.
How is cancer diagnosed?
Most cancers are diagnosed when a person experiences symptoms associated with:
- damage to tissues at the primary site (for example shortness of breath due to tissue destruction in lung cancer);
- damage to nearby tissues or organs;
- activity of the tumour itself (for example, abnormal production of hormones)
- bleeding or infection where the tumour has damaged adjacent surfaces (for example, bleeding in cancer of the large bowel); and
- blockage of bodily functions (for example, bowel obstruction in cancer of the large bowel) [2, 3].
Clinical information is important to the diagnosis of cancer, which is usually confirmed by special tests (for example, a chest x-ray for lung cancer or examination of cells from a cancerous lump in the breast) [2, 3].
Even before a person has symptoms from a cancer, it may be detected by what are called ‘screening tests’ [2, 3]. Examples are Pap smears for cervical cancer or colonoscopy for bowel cancer. (Colonoscopy involves the insertion by a doctor of a long, flexible, lighted tube into a person’s back passage to look at the inside of their bowel.)
References
1 American Cancer Society (2004) What is cancer? Retrieved 23 May 2007 from http://www.cancer.org/docroot/CRI/content/CRI_2_4_1x_What_Is_Cancer_72.asp
2 Crowley L (2007) An introduction to human disease: pathology and pathophysiology correlations. 7th ed. Boston, MA: Jones and Bartlett
3 Kumar V, Abbas A, Fausto N (2004)
Pathologic basis of disease. 7th ed. Philadelphia, PA: Elsevier Incorporated
4 Australian Institute of Health and Welfare (2006) Australia's health 2006: the tenth biennial health report of the Australian Institute of Health and Welfare. (AIHW catalogue no. AUS 73) Canberra: Australian Institute of Health and Welfare
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