Breast cancer is the uncontrolled growth of malignant breast tissue. It is the most common type of cancer in Canadian women.

How Cancer Cells Grow:

• Normally, the cells in our body grow and divide in a controlled manner to replace older, damaged cells.
• Sometimes cells begin to grow and divide in an uncontrolled manner. When this happens, they can form either benign (non-cancerous) or malignant growths (tumours).
• Benign growths will grow to a certain size, but will not spread to other parts of the body, and are generally considered harmless.
• Malignant (cancerous) growths will not stop growing and may eventually invade surrounding tissues or travel to other sites in the body (metastases).

How Breast Cancer Develops:

When hormone levels change during puberty, menopause and with menstrual cycles, as well as during pregnancy and lactation, many women develop breast lumps - most of which are not cancerous. Any lump that does not completely disappear after one of these occasions should be assessed. In post-menopausal women, any new lump or changes in an existing lump should be assessed by a health care professional. See Also: Signs & Symptoms

Cancerous breast lumps (tumours) usually arise from the cells of milk glands or milk ducts. However, malignant tumours occasionally develop within the supporting structures/tissues of the breast.