The sentinel lymph nodes are the first draining lymph nodes from the breast. They are usually located in the armpit (the axilla).
The sentinel lymph node biopsy attempts to find these lymph nodes by injecting a radioactive dye (with or without additional blue dye) into the breast a few hours before surgery. The dye travels through the lymphatic channels of the breast, and concentrates in the first draining lymph nodes – the sentinel lymph nodes.
These lymph nodes (usually 1-4 in number) are removed during surgery, so that they can be examined by the pathologist. This examination may be done at the time of the surgical procedure or later. If there is no tumor in these lymph nodes, no additional lymph nodes need to be removed. However, if tumor cells are detected in these first draining lymph nodes, removal of additional lymph nodes (a complete axillary lymph node dissection) may be required.
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