The breast is the tissue covering the chest or pectoral muscles. The glandular tissue is made up of 15 to 20 sections called lobes, and each lobe has smaller structures called lobules. This entire network of lobes and lobulesis linked by thin tubes called ducts. The breast also contains a network of blood vessels, lymph vessels, and lymph nodes. This network drains lymph fluid and transports white blood cells. Groups of lymph nodes are found near the breast, under the arm, in the chest, and above the collar bone.