Cancer: what is it?

cancer - what is it?

Cancer is a group of diseases resulting from the abnormal growth of some cells that start to divide uncontrollably and can invade and destroy normal tissue.

Throughout our lives, healthy cells in our bodies divide and replace themselves in a controlled sequence. Sometimes, however, a cell begins to divide abnormally for no apparent reason. Abnormally dividing cells that can invade tissues and spread to other parts of the body are cancerous (malignant). The spread of 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.

Tumour formation

A tumour or lump is a cluster of abnormally dividing cells. Most, but not all, cancers form tumours.

Benign (non-cancerous) tumours do not invade healthy tissue or spread to other areas of the body.

Malignant or cancerous tumours can:

  • crowd out or invade 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.

Types of cancer

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, result in different symptoms, and vary in aggressiveness (the speed at which they spread). Some of the types of cancer include the following.

  • 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 start in white blood cells called lymphocytes, which are part of the immune system. These cancers affect the lymphatic system (a network of lymph nodes and vessels that is an important part of the body's immune system).

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.

Risk factors

Risk factors contribute to cancer; however, cancer is not usually caused by one single factor. Most commonly, cancer 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.

Environmental factors

Certain environmental factors can increase your risk of developing cancer.

  • Smoking – people exposed to tobacco 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.
  • Overexposure to ultraviolet light from sunlight or sunlamps increases the risk of 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

  • Diet is associated with cancer risk. For example, a diet that is high in red meat and processed meats increases the risk of bowel cancer. Diets that are high in vegetables, fruit and fibre can help protect against cancer.
  • Being overweight or obese is linked to an increased risk of certain types of cancer.
  • Heavy or regular consumption of alcohol is associated with increased risk of some cancers, including cancer of the mouth, liver, bowel and breast.

Infection

Some infections are associated with an increased risk of certain cancers. For example, certain strains of Human Papillomavirus (HPV) can cause cervical cancer, and long-term infections with Hepatitis B or Hepatitis C viruses can cause liver cancer.

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 person to person.

Last Reviewed: 18 December 2015
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References

1. National Cancer Institute. US National Institutes of Health. What is cancer? http://www.cancer.gov/about-cancer/what-is-cancer (updated 9 Feb 2015). http://www.cancer.gov/about-cancer/what-is-cancer (accessed Dec 2015).
2. Cancer Council Australia. What is cancer? (updated 10 Nov 2015). http://www.cancer.org.au/about-cancer/what-is-cancer/ (accessed Dec 2015).
3. American Cancer Society. What is cancer? (updated 15 Apr 2015). http://www.cancer.org/cancer/cancerbasics/what-is-cancer (accessed Dec 2015).
4. National Cancer Institute. Infectious agents (updated 29 Apr 2015). http://www.cancer.gov/about-cancer/causes-prevention/risk/infectious-agents (accessed Dec 2015).
5. Cancer Council Victoria. Healthy eating to reduce cancer risk (updated May 2014). http://www.cancervic.org.au/downloads/cpc/obesity/healthy_eating_infosheet.pdf (accessed Dec 2015).
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