Cancer is the name given to a large group of diseases, all of which have one thing in common: cells that are growing out of control. Normally, the cells that make up all of the parts of our bodies go through a predictable life cycle -- old cells die, and new cells arise to take their place. Occasionally, this process goes awry, and cells begin to multiply out of control. The end result is a mass of cells, called a tumor. A benign tumor is one that does not spread, or metastasize to other parts of the body. It is considered noncancerous. A malignant tumor, on the other hand, can spread throughout the body and is considered cancerous. When malignant cells break away from the primary tumor and settle into another part of the body, the resulting new tumor is called either a metastasis or a secondary tumor.
There are several major types of cancers: carcinomas form in the cells that cover the skin or line the mouth, throat, lungs and organs; sarcomas are found in the bones, muscles, fibrous tissues and some organs; leukemia is found in the blood, the bone marrow, and the spleen; and lymphomas are found in the lymphatic system.
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