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Cancers are named after the body part from which they originate. Breast cancer originates in breast tissue. Cells in the body reproduce (divide) only when cells are needed. If cells in a part of the body grow and divide out of control, they create a mass of tissue called a tumor. Normal cells that grow out of control are known as benign (not cancerous) tumors. Abnormal cells growing out of control, that don't function like the body's normal cells are called malignant (cancerous) tumors. Cancer can grow and invade surrounding tissue. It can also travel to other parts of the body and form new tumors. This process is termed metastasis.