Cells in the body normally divide (reproduce) only when new cells are needed. Sometimes, cells in a part of the body grow and divide out of control, which creates a mass of tissue called a tumor. If the cells that are growing out of control are more normal cells, the tumor is called benign (not cancerous). If, however, the cells that are growing out of control are abnormal, don’t function like the body’s normal cells, and begin to invade other tissue, the tumor is called malignant (cancerous).
Cancers are typically named after the part of the body from which they originate. Breast cancer originates in the breast tissue. Like other cancers, breast cancer can invade and grow into the tissue surrounding the breast. It can also travel to other parts of the body and form new tumors, a process called metastasis.