The body is made up of many types of cells. Normally these cells grow, divide, and produce more cells as needed to keep the body healthy and functioning properly.
Normal cells constantly reproduce themselves throughout a person's life, but they do so in a systematic and controlled manner. Usually normal cell growth occurs, so worn out tissues can be replaced and wounds repaired.
Sometimes, however, this process goes off track and cells start to grow out of control. They form a mass, and this mass is called a tumour. Tumours can be either benign or malignant.
Cancer is an illness in which abnormal cells in organs and tissues in the body grow out of control. These cells grow and increase in prolific numbers over a period of time. Cancer cells invade and destroy the tissue surrounding them. They split away from a malignant tumour and enter the bloodstream or lymphatic system. (These are the tissues and organs that produce, store, and carry white blood cells which fight infection and other diseases).
This process is called metastasis and it is how cancer spreads from the original (primary) tumour to form new (secondary) tumours in other parts of the body.
Benign tumours are not cancerous. They can usually be removed and, in most cases, they don't come back. Cells in benign tumours do not spread to other parts of the body and most significantly, benign tumours are rarely a threat to life.
Cancer can originate almost anywhere in the body.
Carcinomas, the most common types of cancer, arise from the cells that cover external and internal body surfaces. Lung, breast, and colon are the most frequent cancers of this type in the United States.
Sarcomas are cancers arising from cells found in the supporting tissues of the body such as bone, cartilage, fat, connective tissue, and muscle.
Lymphomas are cancers that arise in the lymph nodes and tissues of the body's immune system.
Leukemias are cancers of the immature blood cells that grow in the bone marrow and tend to accumulate in large numbers in the bloodstream.
Illustration: William Blaske, Michael Binding Satan