Cancer is a group of diseases in which cells in the body grow, change, and multiply out of control. A group of rapidly dividing cells may form a lump or mass of extra tissue. These masses are called tumors.
Malignant tumors penetrate and destroy healthy body tissues.
A group of cells within a tumor may also break away and spread to other parts of the body. Cells that spread from one region of the body into another are called metastases . The term, breast cancer, refers to a malignant tumor that has developed from cells in the breast. The breast is also made up of lymphatic tissue-immune system tissue that removes cellular fluids and waste. There are several types of tumors that may develop within different areas of the breast.