Radio-guided Sentinel Lymph Node Biopsy

Dr. Halsted, in the late 19^th century, presented his original series on the surgical treatment of breast cancer advocating radical mastectomy with total removal of the breast, pectoral muscles and axillary lymph nodes.  However, his series was based on only about 30 patients and lacked any long-term follow up.  Nevertheless, he revolutionized the treatment of breast cancer with his radical surgical approach and most surgeons followed his principles for nearly 100 years.

Over the past 20 – 30 years it has become apparent that this type of radical surgery does not improve survival or cure rates for breast cancer patients and thus there has been a trend for less radical surgery.  This has resulted in the development of the modified radical mastectomy, which spares the chest wall muscles and has been the mainstay of surgical treatment for breast cancer for most of the latter half of this century.

With improvements in chemotherapy and radiation therapy it has been found that patients with early stage breast cancer can be treated adequately with less disfiguring surgery and thus partial mastectomy with axillary nodal dissection, thus sparing these patients the disfigurement of total mastectomy.  

Moreover, the role of axillary dissection has changed.  Whereas, the older philosophy of complete extirpation of all axillary nodal tissue with the intent of eradicating any occult disease that may be present in the axilla has been supplanted by the newer understanding that this does not alter the course of the disease and only leads to debilitating morbidity, i.e. refractory lymphedema of the arm.  Nevertheless, the surgeon does need to know whether or not there is cancer present in the lymph nodes of the armpit to determine whether or not chemotherapy is indicated and what type.  Thus, most surgeons nowadays perform what is really an axillary nodal sampling, which removes many, but not all of the axillary nodes.  Though this procedure has less of an incidence of lymphedema, the incidence is still high.  Additionally, up to 80% of patients with early breast cancer have negative axillary nodes.   This means that 80% of breast cancer patients undergo a procedure which has significant morbidity and from which they receive no real benefit.

New understanding of the mechanism of spread of cancer in lymph node basins over the past few years has resulted in the development of a new procedure which can spare many patients this morbidity and yet yield the information needed to determine the need for chemotherapy in these patients.  It has been found that breast cancer, rather than spreading randomly into the axillary nodes, spreads in a relatively orderly fashion first through a sentinel node before becoming more generally disseminated.  The sentinel node is simply the first node in a chain of nodes. If one can imagine a string of pearls, the cancer has to go through the first pearl to get to the rest.   This is not a perfect analogy since the anatomy of the lymphatic system is more complicated than this, but it works to illustrate the point.

Unfortunately, the surgeon cannot distinguish the sentinel node on physical appearance alone compared to other lymph nodes and unlike the textbook they are not labeled.  What has been discovered is that if the area around the tumor is injected with a radioactive isotope or a special blue dye, these are taken up into the lymphatics and distributed to the lymph nodes in an orderly, time dependent fashion, the sentinel node being first.

On the day of the proposed procedure the patient having been diagnosed with early stage breast cancer by biopsy, is first sent to the nuclear medicine suite where the area around the tumor is injected with a radioactive isotope.  New protocols allow for injection of the skin in the quadrant of the tumor as this has been found to be easier, more reliable and gives equivalent results in some series.  Some surgeons have a lymphocintogram performed.  Though this study may yield some information it is not absolutely necessary.

Next the patient is brought to the OR suite, usually 2 – 4 hours after injection.  Following the induction of anesthesia, the area around the tumor or the skin overlying the tumor is again injected with the blue dye.  Using a special gamma probe, like a Geiger counter, but much more refined, the area of radioactivity in the axilla is localized and the incision made.  A search is then begun for a blue lymphatic vessel running into a blue node.    This node is then excised and counted with the gamma probe outside of the body.  A sentinel node is considered a node, which is hot and/or blue.  There are many technical aspects to this part of the procedure, which for simplicity sake I will not describe here.  Following excision of the sentinel nodes and axillary sampling which I will explain below, the tumor is then excised via partial mastectomy or total mastectomy as dictated by the size and location of the tumor.

At times, because of interference with the gamma probe from the injection site in the breast it may be necessary to remove the tumor prior to localizing the sentinel node with the gamma probe.

Standard pathologic examination of axillary nodal tissue involves 1 or 2 sections of each of 20 to 30 nodes examined microscopically using standard techniques.  Sentinel lymph nodes are examined in as many as 10 sections using very specialized techniques involving the linkage of tumor specific antibodies to a dye.  This process, called immunohistochemistry is extremely sensitive of detecting the smallest deposit of metastatic cancer cells within a lymph node.  However, this process is expensive and time consuming and cannot be applied routinely to as many as thirty lymph nodes removed during standard axillary dissection.  However, when examining 1 or 2 lymph nodes removed using the above-described technique, this type of hyper-scrutiny can be employed.   This allows for detection of metastatic deposits of cancer in the lymph nodes of some patients in whom this diagnosis would otherwise be missed, and thus appropriate treatment withheld.

The current state of the art in the community hospital setting is that a surgeon performing radio guided sentinel lymph node biopsy will complete axillary sampling any way.  This is because this is a very new procedure and still is not the standard of care.  One would not be doing justice to a patient by excising only a misidentified sentinel lymph node that is found to be pathologically negative only to find later that the patient develops metastatic breast cancer in the axilla.   Nevertheless, there is great benefit to the patient in the meticulous examination of the identified sentinel nodes using the techniques of immunohistochemistry and allowing detection of micrometastasis that would have been missed using standard pathologic techniques. Ultimately, once confidence and experience with these technologies is gained, patients will have only the sentinel nodes removed and those patients whose nodes are pathologically negative by immunohistochemistry will require no additional surgery to the axilla. Thus, as many as 80% of patients undergoing axillary dissection for breast cancer would be spared the potential complication of unremitting arm swelling.

As always, I welcome correspondence and questions.

Steven P. Shikiar, MD, FACS email