What is cancer?

Cancer is the abnormal growth, reproduction and spread of cells derived from normal tissues in the body. There are about 200 different kinds of cancers.

Cells normally grow, reproduce and die in response to signals inside and outside the body in an orderly way. Cells that divide when new cells are not needed form too much tissue. This mass of extra tissue can be benign (non-cancerous) or malignant (cancerous). Malignant tissues can invade and damage other tissues and organs. Cancer cells can then break away from the tumour and enter the bloodstream or lymphatic system, spreading the cancer to other parts of the body.

A normal cell can become a cancer cell for no apparent reason or because of repeated or heavy exposure to a carcinogenic, or cancer-causing, substance such as tobacco or alcohol.

Apart from some cancers which are particularly common in childhood, most adult cancers become more common as we get older. It is believed that the risk of losing control over normal cell division increases with increasing age.

The mutated cell divides into two new mutated cells that divide into four mutated cells. This process continues until the mutated cells form a mass called a tumour.


A tumour can be benign or malignant.

A benign (non-cancerous) tumour is self-contained and the mutated cells will not invade surrounding tissue or travel through the bloodstream to other sites. A self-contained tumour, such as a wart, is benign and is generally not life-threatening and usually can be surgically removed.

A malignant (cancerous) tumour is where tumour cells grow and divide, damage surrounding normal cells, and invade other body sites. The greatest danger in a malignant tumour is its ability to spread throughout the body — a process called metastasis.


Metastasis is where the tumour cells grow, divide and eventually enter the bloodstream, and travel to other body sites, implanting themselves in healthy tissue and growing into new malignant tumours.

Gradually, with the progression of the cancer, healthy cells die and the patient's health and functions deteriorate, often resulting in death.

Most malignant cancers fall into one of three main groups:


A carcinoma is a cancer that arises in the skin, the colon (large bowel), the rectum, the bronchial tubes, the ducts of the pancreas or gall-bladder, or the milk ducts of the breast. A carcinoma can be found on any lining surface in the body.


A sarcoma is a cancer that arises from the substance of solid tissues such as muscle, bone, lymph glands, blood vessels and fibrous and other connective tissues. Bone cancer is an example of a sarcoma.

Leukaemia and lymphoma

Leukaemias are also classed as malignant (cancerous) growths. Leukaemia is a cancer that originates from blood-forming cells, while a lymphoma originates from cells within the immune system.

What are the symptoms of cancer?

Because cancer includes many different conditions that may affect many different organs or systems within the body, the range of symptoms that can be produced by cancers is vast. The symptoms depend on the location of the tumour, they tissue it originates from and the rate of growth. Symptoms may be caused by the tumour itself or the effect of the tumour on surrounding tissues, for example obstruction or bleeding into the bowel, lung or urinary tract. Unexplained weight loss is a feature of many cancers.

There are some important warning signals that warrant investigation. If you develop any of the following symptoms, you should report them to your doctor:

Remember that there may be other causes for these symptoms. But if they are caused by cancer, the sooner you seek medical advice the better as early detection increases the chances of cure.

What is the outlook?

Almost half of all cancers can be completely cured and the survival rates for the various cancers continue to improve. Cure and survival rates and the chances of recurrences do differ considerably, however, depending on the type of cancer and the stage at diagnosis.

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