What is Breast Cancer?

Normal breast cells grow and divide in a controlled manner to replace cells that have died because of damage or age. Breast cancer is a disease in which abnormal breast cells increase in size, divide and destroy normal tissue. The cancer cells grow out of control for several months or years before they are large enough to be found on a mammogram or felt as a lump. The result is a mass, or tumour, that may continue to grow and spread at the expense of normal cells if not removed by surgery and/or controlled with medication.

By the time breast cancer is found, it already has many millions of cells. Screening mammograms done in women over 50 years old sometimes find the lump before it can be felt. The most common way for breast cancer to spread is through the lymphatic channels to the lymph nodes in the axilla (armpit). The normal role of these lymph nodes is to drain fluids from the breast and arm.