Cancer is a disease of the cells, which are the basic building blocks of the human body. The body constantly makes new cells to help us grow, replace old cells and heal injuries.
Sometimes this process goes wrong, and the cell becomes abnormal. The abnormal cell keeps dividing, making more abnormal cells, which can gather together and form a lump called a tumour. There are two kinds of tumours:
- Benign tumours are not cancer. They do not spread to other parts of the body.
- Malignant tumours are cancer. They can spread to other parts of the body.
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Where cancer starts
As our body is made up of cells, cancer can start anywhere in the body. Some common places for cancer to start include the skin, bowel, breasts, prostate and lungs. The place where the cancer first starts is called primary cancer.
Sometimes the doctors can’t find where the cancer first started. This is called cancer of unknown primary.
How cancer spreads
Sometimes cancer cells move to other parts of the body. Cancer that has spread and developed into a tumour somewhere else in the body is called a secondary cancer or metastasis.
Cancer can happen to anybody. Some things put people at a greater risk of getting cancer include:
Injury or stress does not cause cancer. Cancer is not caused by being a bad person and it does not mean that you or your family are bad people. Cancer is also not contagious. People can’t catch it from someone who has it, and it is safe to be near someone who has cancer.
Sometimes, doctors find cancer because the person is feeling unwell and has symptoms. It is important to know what is normal for your body, and to see your doctor straight away if you notice changes, including:
- lumps, sores or ulcers that don’t heal
- breast changes, such as lumpiness, a thickened area, unusual nipple discharge, a nipple that turns inwards, a change in shape or colour, or pain
- skin changes, such as moles that change shape, size or colour, or bleed
- a cough that won’t go away
- finding it hard to breathe or voice changes
- losing weight without trying
- nausea or vomiting that doesn’t go away
- diarrhoea or constipation that doesn’t go away or you can’t explain
- for women, loss of blood from the vagina that is not normal, even if it’s a few spots between periods or after menopause
- blood in your poo or wee
- unexplained pain in the body that does not get better.
Many of these symptoms can be caused by common health problems, not cancer. You should see a doctor about any changes or persistent symptoms.
Find out more about specific types of cancer
While cancer is common, many cancers can be treated by a doctor if they are found early. It is important to go to cancer screening programs. Screening for breast, bowel and cervical cancer saves lives because cancer can be found earlier, when it is easier to treat.
Cancer won’t go away without treatment. Cancer treatment depends on the type and stage of the cancer (how much it has grown and spread) and commonly includes chemotherapy, radiation therapy, surgery and immunotherapy. Each person is different, and some people have more than one type of treatment.
If the cancer can't be treated, it is possible that your doctor will give you palliative treatment to make you feel better by controlling your symptoms. With these types of treatment, you might feel less pain and have a better life.
What is Cancer?
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Expert content reviewers:
Dr Karen Taylor, Radiation Oncologist, GenesisCare Radiation Oncology; Cecilia Barling, consumer; Clem Byard, 13 11 20 Cancer Council Victoria.
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The information on this webpage was adapted from What is Cancer? - Information for people affected by cancer (2020 edition). This webpage was last updated in June 2021.