For the last hundred years conventional wisdom has been that the lymph nodes under the arm (axilla) should be removed as part of the surgery for breast cancer. The development of the lumpectomy in the 1970’s, wherein only a portion of the breast is removed (the tumor plus a rim of normal tissue), did not change the concept of lymph-node removal. Oncologists have felt all along that this was probably a useful operation but no one had ever proven the point. With the advent of effective chemotherapy to prevent cancer spread, the results of the lymph node analysis helped in treatment planning; unanswered was whether that therapy obviated the need for the removal of these very nodes.
About fifteen years ago surgeons discovered that if you injected a dye or a radioisotope into the area of the breast that contained the tumor, you could identify which axillary lymph nodes were the first to drain the breast and catch rogue cancer cells. Those lymph nodes are called “sentinel nodes.” If they are free of cancer, most surgeons today do not remove the rest of the nodes in the axilla because data have shown that these nodes will very likely be normal. If the sentinel nodes are positive, conventional wisdom until now has been to remove the rest of the lymph nodes. Recently surgeons asked whether it was necessary to remove these nodes.