Cancer is the name for a group of diseases in which abnormal cells grow and displace normal body tissue. Normally, healthy cells in your body grow, divide, die and replace themselves in an orderly way. This process keeps your body in good repair. Sometimes, cells lose the ability to control their growth. They grow too rapidly without any order, making too much tissue and forming tumors. These tumors can be benign (not cancer) or malignant (cancer).

Benign tumors are not cancer. They will not spread to other parts of your body, and they are seldom a threat to your life. Often, benign tumors can be removed with surgery, and they are not likely to return.

Malignant tumors are cancerous. They can spread and kill nearby tissues and organs. Cancer cells also can break away from the main tumor and enter the bloodstream and the lymphatic system. This process of cancer spreading to other parts of your body is called metastasis. Even if a malignant cancer tumor is removed from your breast, the disease may return if the cancer cells had spread to other parts of your body before the tumor was removed.