Sometimes normal, healthy cells lose the ability to control their growth. Although they do not develop normally and cannot do the job they are supposed to do, they keep multiplying. When the abnormal cells join together to form a tumor that invades and eventually destroys surrounding healthy tissue, the disease is called cancer.
Cancer can begin in any organ or tissue of the body.
The original tumor is called the primary cancer or primary tumor and is usually named for the part of the body in which it begins. Cancer cells can break away from a primary tumor and travel through the blood or lymphatic system to other parts of the body. The spread of cancerous cells is called metastasis. The cancerous cells may build up in lymph nodes near the primary tumor, or they may travel to distant parts of the body. When this happens, the disease is called metastatic breast cancer and the new tumor is called a secondary tumor.