A sentinel lymph node is the first lymph node to receive drainage from the breast that could potentially have cancer cells from a primary invasive breast cancer. There are usually 1-3 sentinel lymph nodes. ⁠ ⁠ We check the sentinel lymph node at the time of surgery for invasive breast cancers for both patients undergoing a lumpectomy or mastectomy. We either inject a radioactive tracer, blue dye, or both into the breast or around the area of the tumor. ⁠ ⁠ This helps us to figure out which lymph nodes are the first to receive drainage from the breast and those lymph nodes that could be first to be invaded by breast cancer cells. We typically remove between 1-3 lymph nodes. If the lymph node(s) are positive we may remove the other nodes. ⁠ ⁠ This is called an axillary node dissection. Before the 1990s we removed all the lymph nodes if you were diagnosed with breast cancer.⁠ ⁠ As you can imagine, a lot of women did not have any cancer in those lymph nodes, but ended up with significant arm swelling also know as lymphedema. With the development of the sentinel lymph node for the breast, we have reduced the morbidity of axillary surgery because we realized that if the sentinel node was negative, it is very highly unlikely the rest of the nodes upstream from the sentinel lymph node would be positive. ⁠ ⁠ The invention of the sentinel lymph node revolutionized the way the surgical oncology community treated breast cancer and has prevented post-surgical complications for so many countless patients. ⁠