Cancer… is a distorted version of our normal selves.
Harold Varmus, 1989

All cancers begin in cells, the body's basic unit of life. To understand cancer, it is important to understand how a normal cell in the body becomes a cancer cell.

The body is made up of trillions of living cells. Each cell in our body has a certain job to do. Normal body cells grow, divide, and die in an orderly fashion. They die when they are old or damaged, and then they are replaced with new cells.

However, sometimes this orderly process goes wrong. The genetic material (DNA) of a cell can become damaged or changed, producing changes(mutations) that affect normal cell growth and division. When this happens, cells do not die when they should and new cells form when the body does not need them. These extra cells may form a mass of tissue called a tumour.

Abnormal cell division could begin in any part of the body and at any time depending on the factors that cause the mutations. Cancer is therefore not just one disease but a group of diseases characterised by abnormal cells dividing without control. Tumours that form in the body are not always cancerous.

Benign tumours (localised tumours that do not spread) are considered non-cancerous while malignant tumours (tumours that spread to other parts of the body) are considered cancerous. In case of malignant tumours, cancer cells sometimes breakaway from the primary tumour where they originated and spread to other parts of the body through the blood and lymph systems. To sustain themselves through this journey they plunder the body’s normal sources of blood and oxygen depriving the body’s normal cells of their sustenance and in turn causing them to atrophy. Thus something that begins as a normal bodily function could grow into something that harms the body itself. Cancer has therefore been called "a distorted version of our normal selves".

There are more than 100 different types of cancers. In order to make classification easier, most cancers are named for the organ or type of cell in which they start. For example cancers that begin in the breast are called breast cancer. Cancers that are named for the type of cell in which they originate are grouped into five main categories.

  • Carcinoma - cancer that begins in the skin or in tissues that line or cover internal organs
  • Sarcoma - cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue
  • Leukaemia - cancer that starts in blood-forming tissue such as the bone marrow and causes large number of abnormal blood cells to be produced and enter the blood
  • Lymphoma and myeloma - cancer that begins in the cells of the immune system
  • Central nervous system cancers - cancer that begins in the tissues of the brain and spinal cord