What is cancer?
The body is made up of trillions of living cells. Normal body cells grow, divide into new cells, and die in an orderly way. During the early years of a person’s life, normal cells divide faster to allow the person to grow. Once the person becomes an adult, most cells divide only to replace worn-out, damaged, or dying cells.
Cancer begins when cells in a part of the body start to grow out of control. There are many kinds of cancer, but they all start because of this out-of-control growth of abnormal cells.
Cancer cell growth is different from normal cell growth. Instead of dying, cancer cells keep on growing and form new cancer cells. In most cases the cancer cells form a tumor. Cancer cells can also grow into (invade) other tissues, something that normal cells can’t do. Being able to grow out of control and invade other tissues is what makes a cell a cancer cell.
Sometimes cancer cells spread to other parts of the body. There they begin to grow and form new tumors. This process is called metastasis.
No matter where a cancer spreads, it is named (and treated) based on the place where it started. For instance, prostate cancer that has spread to the bones is still prostate cancer, not bone cancer.
Different types of cancer can behave very differently. They grow at different rates and respond to different treatments. That is why people with cancer need treatment that is aimed at their own kind of cancer.
Not all tumors are cancerous. Tumors that aren’t cancer are called benign. Benign tumors can cause problems-- they can grow large and press on healthy organs and tissues. But they can’t grow into other tissues. Because of this, they also can't spread to other parts of the body (metastasize). These tumors are rarely life threatening.
Last Medical Review: 01/09/2015
Last Revised: 01/30/2015