Breast cancer is a malignant tumor that starts in the cells of the breast. It is a group of cancer cells that can grow into (invade) surrounding tissues or spread (metastasize) to distant areas of the body. The disease occurs almost entirely in women, but men can develop it, too.
Worldwide, breast cancer is the most frequently occurring malignant tumor diagnosed and the principal cause of death in women. Nearly half of the recently diagnosed cases of breast cancer can be explained by known risk factors such as menarche, the first live birth, menopause and proliferative breast disease.
Another 10% of these cancers are associated with a positive family history. Additionally, the risk can be affected by lifestyle, demographic factors, and the environment although these factors cannot be clearly demonstrated.