The sentinel node is the first lymph node in the chain of lymph nodes that drain the region of the breast where a cancerous tumor was found. If no tumor cells are found in the sentinel lymph node, then it is very unlikely that further lymph nodes will contain metastases. When tumor cells are found in the sentinel lymph node, further lymph nodes are removed. The sentinel node is found by injecting a small amount of a radioactive substance (Technetium) and a blue dye prior to surgery. These substances are taken up by the lymphatic system and collect in the sentinel node.
The sentinel node or nodes are surgically removed. In most cases the complete axillary node dissection and postoperative edema of the arm can be avoided. Due to its accuracy and low side effect profile, the sentinel node biopsy is a recommended standard procedure for staging breast cancer.