It is characterized by the uncontrolled growth and spread of abnormal cells, which usually starts in the milk sacs or ducts. The tumour may be hard or soft and may sometimes be described as a thickening of the breast.
Breast cancers are almost always painless.
It rarely affects men. One woman in nine will develop breast cancer by age 85. It is the second leading cause of cancer deaths in women, after lung cancer. It is the leading cause of cancer death among women aged 40 to 55. Women's Health Matters is a trademark of Women's College Hospital Foundation, which Sunnybrook and Women's College Health Sciences Centre is licensed to use.