Cancer is a group of diseases that cause cells in the body to
change and grow out of control. Most types of cancer cells eventually
form a lump or mass called a tumor, and are named after
the part of the body where the tumor originates.
The vast majority of breast cancers begin in the parts of the
breast tissue that are made up of glands for milk production,
called lobules, and ducts that connect the lobules to the nipple.
The remainder of the breast is made up of fatty, connective, and
lymphatic tissues.
Breast cancer is typically detected either during a screening
examination, before symptoms have developed, or after a
woman notices a lump. Most masses seen on a mammogram
and most breast lumps turn out to be benign; that is, they are
not cancerous, do not grow uncontrollably or spread, and are
not life-threatening. When cancer is suspected, microscopic
analysis of breast tissue is necessary for a definitive diagnosis
and to determine the extent of spread (in situ or invasive) and
characterize the type of the disease. The tissue for microscopic
analysis can be obtained via a needle or surgical biopsy. Selection
of the type of biopsy is based on individual patient clinical
factors, availability of particular biopsy devices, and resources.