What is Cancer?

Posted: Aug. 1, 2004

There are over 100 types of cancer diseases.

Cancer affects our cells, the body’s basic unit of life. To understand cancer, it is helpful to know what happens when normal cells become cancerous.

The body is made up of many types of cells. Normally, cells grow, divide, and produce more cells as they are needed to keep the body healthy and functioning properly. Sometimes, however, the process goes astray – cells keep dividing when new cells are not needed. The mass of extra cells forms a growth or tumor. Tumors can be either benign or malignant.

Benign tumors are not cancer. They often can be removed and, in most cases, they do not come back. Cells in benign tumors do not spread to other parts of the body. Most important, benign tumors are rarely a threat to life.

Malignant tumors are cancer. Cells in malignant tumors are abnormal and divide without control or order. These cancer cells can invade and destroy the tissue around them. Cancer cells can also break away from a malignant tumor. They may enter the bloodstream or lymphatic system (the tissues and organs that produce and store cells that fight infection and disease). This process, called metastasis, is how cancer spreads from the original (primary) tumor to form new (secondary) tumors in other parts of the body.

Source: National Cancer Institute

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