What is Cancer?

Normal human cells grow, divide, and die in a predictable and orderly way. As our bodies grow and develop in childhood and adolescence, our cells divide rapidly. Once we become adults, most cells divide only to replace dying cells or to repair injuries.
Cancer cells are different. Because of genetic mutations (changes) caused by exposure to cancer-causing agents they continue to grow and divide, even when your body does not need new cells. As cancer cells grow and divide, they form a disorganized mass made of billions of cells called a tumor. A tumor can be harmful (malignant) or harmless (benign) to your body. A malignant tumor is cancer.

Cancer cells can penetrate and damage adjacent organs and tissues, a process known as invasion. Cancer cells may also break away from a malignant tumor and spread to other parts of the body through the bloodstream or lymphatic system. This is called metastasis.

Learn About a Specific Type of Cancer

Content Updated: April 27, 2014

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