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About Cancer

The word cancer refers to a group of almost 200 different diseases.

Most cancers are named for the part of the body where they begin. They keep that name even if the cancer spreads to another part of the body. For example, cancer that starts in the breast is still called breast cancer if it spreads to the lungs.

Some cancers do not form tumors. For example, leukemia is a cancer of the bone marrow and blood.

Learn about signs and symptoms of cancer.

How Cancer Starts

Our bodies are made up of many types of cells. When they work as they should, cells grow and divide to produce more cells as they are needed. When cells become old or damaged, they die and are replaced with new cells. This keeps our bodies healthy.

Sometimes, cells keep dividing when new cells are not needed. These extra cells may form a mass, called a growth or tumor. A tumor may be benign (non-cancerous) or malignant (cancerous).

What Causes Cancer?

Cancer has no single cause. We know some lifestyle factors that increase the risk of cancer, such as chemicals in cigarette smoke and radiation from the sun. But there is no way to know all the factors that started a person’s cancer.

We do know that cancer is not contagious—you cannot catch it from someone else. There is currently no evidence that high levels of stress or anxiety cause cancer.

Learn more about risk factors of cancer and ways to screen for and prevent cancer.

How Cancer Spreads

Cancer cells crowd out healthy cells, keeping them from doing their jobs. Cancer cells can also invade nearby tissue or spread to other areas of the body to create new tumors. This spread of cancer cells is called metastasis.

Cancer can spread in three ways: through tissue, the lymph system, and the blood.

  1. Tissue. The cancer spreads from where it began by growing into nearby areas.
  2. Lymph system. Cancer cells travel through the lymph vessels to other parts of the body.
  3. Blood. Cancer cells move through blood vessels to other parts of the body.

Cancer Staging

The stage of cancer tells how much cancer is in the body and if it has spread. Knowing the stage of a cancer helps us make the best treatment plans.

Learn more about the stages of cancer from the National Cancer Institute.