What is cancer?
Reviewed by: Annie Angle cancer nurse, Dip. Oncology Nursing, Royal Marsden, London
Cancer is a disease of the body's cells. Our bodies are always making new cells: so we can grow, to replace worn-out cells, or to heal damaged cells after an injury. This process is controlled by certain genes. All cancers are caused by changes to these genes. Changes usually happen during our lifetime, although a small number of people inherit such a change from a parent.
Normally, cells grow and multiply in an orderly way. However, changed genes can cause them to behave abnormally. They may grow into a lump. These lumps can be benign (not cancerous) or malignant (cancerous).
Benign lumps do not spread to other parts of the body.
A malignant lump (more commonly called a malignant tumour) is made up of cancer cells. When it first develops, this malignant tumour is confined to its original site. This is called the primary cancer. If these cells are not treated they may spread into surrounding tissue and to other parts of the body.
Cancer spread
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. For a cancer to spread, cells from the primary cancer must break away, move to another part of the body and begin to grow there. The cells travel through the body because cancer cells are able to move more freely than normal cells. They also make substances that stimulate them to move. Cancers can move in three main ways:
- locally: the cancer grows directly into nearby tissue
- to distant organs: through the blood circulation
- to distant organs: through the lymphatic system.
For the cancer to spread through the lymphatic system or blood, a cancer cell must break away from the primary tumour. The cell then begins its journey through the blood or lymphatic system. It is a complicated process and many cells do not survive the ‘trip'. However, if they do they will eventually end up in the tissue of another organ in the body. Here another cancer will begin to grow (a ‘secondary cancer').
For a cancer to grow bigger than the head of a pin, it must grow its own blood vessels. This is called angiogenesis.
The beginnings of cancer
How cancer spreads
Can you catch cancer from someone else?
Cancer is not contagious
Cancer is not infectious (contagious) so you can't catch it from someone who has it. It is quite safe for you to be with someone who has cancer. Touching people with cancer is also safe. Their cancer happened because they had cell changes in their body. This cannot be passed on to anyone else.
The only time you need to be careful around someone with cancer is if they have been treated with brachytherapy. Brachytherapy is when thin tubes, seeds or rods containing radioactive material are put in the body. This sends some radiation outside the body. Because of the slight risk of people being affected by the radiation, the hospital will limit visits while the person is being treated with brachytherapy.
People receiving normal radiotherapy are not radioactive.
Protect yourself from infections that sometimes can lead to cancer
Find out about what you can do to protect yourself from human papilloma virus (HPV) and hepatitis B. Both of these can cause changes to cells that sometimes lead to cancer.
There's exciting research going on that is looking at certain other viruses, retroviruses and bacteria that have been linked to some cancers. They include H. pylori, HTLV-1 and Epstein-Barr virus. The promise of such research is that preventive vaccines and effective treatments may be developed in the future.
Cancer symptoms
Cancer symptoms depend on where the cancer is in the body. Cancers release chemicals and hormones that can cause symptoms. They can also press on nerves and other body organs causing symptoms such as pain, breathlessness and nausea.
To find out about symptoms of specific types of cancer look in our cancer types section.
Video - What is cancer?
with Professor Richard Bell
Part 1 (7:20)
Part 2 (6:37)
Part 3 (7:57)
Part 4 (6:57)
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