For a sentinel lymph node biopsy: A special blue dye and/or a radioactive substance is injected into the breast to determine which lymph nodes are the first to receive drainage from the breast, as these would potentially be the first to be invaded by cancer cells. If there are cancerous nodes, an axillary (armpit) lymph node dissection may follow depending on how many sentinel nodes are positive or certain pathological characteristics of the nodes. In axillary dissections, the lymph nodes in the armpit are removed and checked to see if more nodes, other than the sentinel nodes have also been affected by the cancer.
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