Updated 16 August 2018

What is cancer?

Cancer is the name given to a collection of diseases caused by abnormal or uncontrolled cell growth.

Cancer is not just a single disease, but a name given to a collection of related genetic diseases. One in six South African men and one in seven South African women will get cancer in their lives.

It is a life-threatening condition and can affect anyone at any stage in their lives. Cancer treatment, although increasingly successful over the past few decades, can be both painful and uncomfortable.

The Cancer Association of South Africa (CANSA) defines cancer as “any malignant growth or tumour caused by abnormal and uncontrolled cell division. If not stopped, it may spread to other parts of the body through the lymphatic system or blood stream”.

All cancers have abnormal cell division as their basis. Cancer can start just about anywhere in the human body.

Human cells have the capacity to grow, and to divide and to form new cells as, where and when they are needed. Old cells die, and the body replaces them. This happens everywhere in the body, from the brain, the skin, the organs, the intestines – in short, all over. However, sometimes old or damaged cells do not die, but they become abnormal and start dividing without stopping. The body usually has a very efficient system that sends messages to old or damaged cells to stop dividing, but every now and then it fails, when the immune system is unable to detect these cells and eliminate them from the body.

These rogue cells can then form what we call "tumours", which are masses of tissue.

But not all cancers form tumours, the National Institute of Health (NIH) explains. Cancers of the blood, such as leukaemia, do not form solid tumours, and spread through the blood stream.

When a tumour originates in the body, invasive cells can break off from and spread to other places in the body through the lymphatic system or the blood stream. That is how someone who is originally diagnosed with lung cancer can also develop cancer of the brain or the liver or the stomach. A cancerous tumour spreads, whereas a benign (harmless) tumour does not. If a benign tumour can be removed, it usually does not grow back, unlike a malignant tumour, which could make a reappearance.

One can have a genetic predisposition to cancer, or cancer-causing environmental substances can cause abnormal cell division in the body.

Read more:

Symptoms of cancer


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CANSA’s purpose is to lead the fight against cancer in South Africa. Its mission is to be the preferred non-profit organisation that enables research, educates the public and provides support to all people affected by cancer. Questions are answered by CANSA’s Head of Health Professor Michael Herbst. For more information, visit

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