© 2005-2012 American Society of Clinical Oncology (ASCO). All
rights reserved worldwide. In the United States, breast cancer
is the most common cancer in women (excluding skin cancer). Men
can also develop breast cancer, but breast cancer in men is
rare, accounting for less than 1% of all breast cancers. About
the breast The breast is mostly made up of fatty tissue. Within
this tissue is a network of lobes, which are made up of tiny,
tube-like structures called lobules that contain milk glands.
Tiny ducts connect the glands, lobules, and lobes, carrying the
milk from the lobes to the nipple, located in the middle of the
areola (darker area that surrounds the nipple). Blood and lymph
vessels also run throughout the breast; blood nourishes the
cells, and the lymph system drains bodily waste products. The
lymph vessels connect to lymph nodes, the tiny, bean-shaped
organs that help fight infection. About breast cancer Cancer
begins when normal cells in the breast change and grow
uncontrollably, forming a mass cal