Sentinel Lymph Node Mapping in Breast Cancer

Dr. Cody presents a very thorough review of the use of sentinel lymphadenectomy in breast cancer. The article raises key issues related to a procedure that is becoming more widespread and may indeed replace axillary dissection for the staging of breast cancer. The sentinel node concept is based on the assumption that if a tumor spreads through the lymphatics, the lymph node that first drains the primary tumor, ie, the sentinel lymph node, will be the node most likely to harbor metastases. It follows that if the sentinel node is free of metastases, there is a high likelihood that the rest of the regional nodal basin will be negative. The validity of this concept was first demonstrated in melanoma by Morton and colleagues using intraoperative lymphatic mapping with blue dye followed by sentinel lymph node dissection.[1] This work provided a model for the investigation of the sentinel node concept in other cancers, particularly breast cancer. Many groups have now published their series of sentinel lymphadenectomy in breast cancer, using modified techniques and either dye, a radiopharmaceutical, or a combination of both as the lymphagogue of choice. The author’s Table 1 summarizes the identification, sensitivity, false-negative, and accuracy rates of the procedure cited in published series. The authors of all of these series achieved excellent results with their particular technique and validated these results by an immediate complete axillary lymph node dissection. As Dr. Cody emphasizes, it is apparent that, regardless of the agent used, the three different approaches are quite comparable. Issues Raised by Memorial Sloan-Kettering Pilot Study Dr. Cody advocates the use of both radiopharmaceutical and blue dye, and he describes a pilot study conducted at Memorial Sloan-Kettering Cancer Center in which all patients underwent lymphoscintigraphy and injection of blue dye followed by radioguided surgery with a handheld gamma probe.[2] We will discuss three issues raised by the results of this pilot study. First, while lymphoscintigraphy was positive in the axilla in only 75% of cases, the radioisotope allowed the detection of the sentinel node alone in 88% of cases. As mentioned in this article, it is interesting that a negative lymphoscintigram does not preclude successful radiolocalization of the sentinel node at surgery. Possible reasons for this phenomenon include the following: either gamma camera imaging or positioning of the patient in nuclear medicine was not optimal; image timing was miscalculated; or soft tissue, skin, and air between the hot sentinel node and camera caused excess scatter and loss of signal that became detectable only by the handheld gamma probe. These are some of the reasons why the role of preoperative lymphoscintigraphy as a routine procedure remains unclear among those who advocate radioguided sentinel lymphadenectomy. Second, it seems artificial to isolate the sentinel node identification rate for each method when, in fact, no patient received either agent alone. Perhaps lymphatic uptake of blue dye is inhibited after the breast has been injected with a large volume of saline and radiopharmaceutical. Finally, we question the inclusion of intradermal injection of radiopharmaceutical as a recommended option in the treatment algorithm, given that Cody’s group did not validate this technique with a complete axillary dissection in their initial study. To date, there are few data supporting the intradermal injection of radiopharmaceutical. This approach needs to be formally evaluated. At the John Wayne Cancer Institute, we have been proponents of the use of blue dye alone, while others profess the advantages of radioisotope injection and localization with a handheld gamma probe, either alone or together with dye. The debate will continue, especially as newer agents emerge for detecting the sentinel node. If a high level of accuracy is achieved with any number of different techniques, the controversy will become moot. The success and accuracy of the chosen technique require validation within each contributing group