About one in every eight women develops breast cancer. When the cancer spreads, it can form new tumors in other parts of the body. These spreading tumors are called metastases. If the cancer spreads through the blood, it most commonly travels to the bones of the pelvis, spine, legs, ribs, and skull. Metastases may also be found in the liver and lungs.
Cancers are uncontrolled growths of abnormal cells.
It is not known why they occur. However, some women are more likely to get them than others. You have never breast-fed a baby or you had your first child after age 30. You started your menstrual periods very early or you went through menopause very late. Using birth control pills and oral estrogen does not seem to increase the risk of breast cancer.