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Use our cancer glossary to learn more.
What is Cancer?
Although there are many kinds of cancer, they all start because of out-of-control growth of abnormal cells. Normal body cells grow, divide, and die in an orderly fashion. Because cancer cells continue to grow and divide, they are different from normal cells. Instead of dying, they outlive normal cells and continue to form new abnormal cells.
When this abnormal cell growth occurs, the result can be the development of a lump, mass or tumor, which can be benign (non-cancerous) or malignant (cancerous). Cancer cells develop because of damage to DNA, which directs all activities in each cell. When DNA becomes damaged, the body is usually able to repair it. In cancer cells, however, the damaged DNA is not repaired.
Cancer comes in many forms, and the specific disease is named for the part of the body in which it begins. Cells from cancerous tumors can spread, or metastasize, throughout the body. For example, cancer that begins in the prostate but has spread to the bones is called metastatic prostate cancer. Some cancers involving the blood and blood-forming organs (bone marrow) do not form tumors, but circulate through other tissues where they grow.