Breast cancer is a disease in which malignant (cancer) cells
form in the tissues of the breast. The breast is made up of
lobes and ducts. Each breast has 15 to 20 sections called lobes,
which have many smaller sections called lobules. Lobules end in
dozens of tiny bulbs that can produce milk. The lobes, lobules,
and bulbs are linked by thin tubes called ducts. Anatomy of the
female breast. The nipple and areola are shown on the outside of
the breast. The lymph nodes, lobes, lobules, ducts, and other
parts of the inside of the breast are also shown. Each breast
also contains blood vessels and lymph vessels. The lymph vessels
carry an almost colorless fluid called lymph. Lymph vessels lead
to organs called lymph nodes. Lymph nodes are small bean-shaped
structures that are found throughout the body. They filter
substances in lymph and help fight infection and disease.
Clusters of lymph nodes are found near the breast in the axilla
(under the arm), above the collarbone, and in the chest. See the
following PDQ sum