Chemotherapy refers to the use of a variety of different drugs that can do as little as slow the growth of cancer cells to as much as kill some, or occasionally, all cancer cells in a patient. Chemotherapy may be given as pills, as an injection, or via an intravenous infusion, depending upon the types of drugs chosen. Combinations of different drugs are usually given, and treatment is administered in cycles with a recovery period following each treatment. There are numerous drugs uses today to treat breast cancer. The same chemotherapy agents used in women for breast cancer can be effective in men. In most cases, chemotherapy is administered on an outpatient basis. Chemotherapy may be associated with unpleasant side effects including fatigue , hair loss , nausea and vomiting , and diarrhea .
The blood supply from the breast comes primarily from the internal mammary artery, which runs underneath the main breast tissue. The blood supply provides nutrients, such as oxygen, to the breast tissue. The lymphatic vessels of the breast flow in the opposite direction of the blood supply and drain into lymph nodes. It is through these lymphatic vessels that breast cancers metastasize to lymph nodes. Most lymphatic vessels flow to the axillary (under arm) lymph nodes, while a smaller number of lymphatic vessels flow to internal mammary lymph nodes located deep to the breast. Knowledge of this lymphatic drainage is important, because when a breast cancer metastasizes, it usually involves the first lymph node in the chain of lymph nodes. This is called the "sentinel lymph node,” and a surgeon may remove this lymph node to check for metastases in a patient with breast cancer.