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Ann Thorac Surg 2006;82:4-5
© 2006 The Society of Thoracic Surgeons
Department of Surgery, Wright State University, Boonshoft School of Medicine, Dayton, Ohio
* Address correspondence to Dr Little, Department of Surgery, Wright State University, Boonshoft School of Medicine, 1 Wyoming St, 7801 WCHE, Dayton, OH 45409 (Email: alex.little{at}wright.edu).
here is undisputed great value in the accurate staging of patients with nonsmall cell lung cancer, as staging results guide therapeutic, particularly multimodality, strategy planning. The article, "Intraoperative, radioguided sentinel lymph node mapping in 110 non-small cell lung cancer patients," addresses the issues of operative and pathologic staging of intrathoracic lymph nodes by reporting an experience in assessing a sentinel lymph node detection technique [1].
As defined by Webster, a sentinel is, "One who watches or guards ... from surprise, to observe the approach of danger and give notice of it." When Morton and coworkers [2] introduced the concept of sentinel node detection in patients with breast cancer and melanoma, their goal was identification of the lymph node that was most likely to harbor metastatic disease and thus give notice of the likelihood of other, more distant, nodes harboring metastases. There are two potential benefits of this technique (ie, one intraoperative and one postoperative). The theoretical intraoperative benefit is the ability to withhold an extensive regional lymphadenectomy when an identified sentinel lymph node is free of metastases. This requires that the node can be examined in real time and that if it is tumor free, the confidence that other nodes will be also. The postoperative benefit is the ability of focusing the pathologic search for metastases and micrometastases on the lymph node most likely to harbor them.
The authors used a radio-guided lymph node mapping technique in 110 consecutive nonsmall cell lung cancer patients to assess the results of that technique. In my opinion, they have shown benefit in regard to the postoperative staging utilization, but not the intraoperative decision-making process. Although the sensitivity and negative predictive value for their technique are both reasonably good, there are patients whose sentinel lymph node was negative on routine pathologic examination with hematoxylin and eosin staining, but in whom other nodes with metastases were found. In addition, all of their pathologic examinations were performed postoperatively, not intraoperatively with frozen sections. So their technique would not serve to eliminate the staging and possibly therapeutic benefit of a mediastinal lymphadenectomy. In addition, it is clear that this is not necessarily an easy technique to master. There is potential for error when intrabronchial tracer is mistakenly identified as lymphatic tissue or when a tracer accumulated in pooled blood leads the surgeon astray. There is enough cumulative potential for inaccuracy that I do not believe that this technique as currently described will be useful in making intraoperative decisions.
On the other hand, when the technique is applied postoperatively to resected lymph nodes, it does seem that the pathologist is very likely to be guided to the lymph node or nodal group most likely to contain metastases. All submitted nodes are examined in standard fashion after hematoxylin and eosin staining of paraffin embedded sections. The importance of the sentinel node technique really lies in allowing the pathologist to focus the search for micrometastases using polymerase chain reactions or immunohistochemistry on one lymph node or a small group of lymph nodes. To examine all resected lymph nodes in this exhaustive fashion is not a realistic proposition. The authors identified this benefit by having 4 patients with micrometastases in sentinel nodes that were not detected with routine hematoxylin and eosin examinations. I think the technique as described by these authors and similarly by Liptay [3] bears continued pursuit and refinement. My previous experience using a dye technique was not encouraging, and I do think that radio-guided mapping has the most potential [4].
Despite any cavils I may have about the technique, the most important point (ie, more than the technical considerations of which tracer, how much tracer to inject, and so forth) is that any encouragement to thoracic surgeons to do adequate lymph node staging is welcome. I stress the benefit of encouraging surgeons performing lung resections to do adequate lymph node staging because I have to disagree with the authors who state that, "Mediastinal lymph node dissection has become an integral part of nonsmall cell lung cancer surgery..." A review of more than 11,000 surgically treated patients with nonsmall cell lung cancer documented that invasive mediastinal staging was insufficiently performed, either before or during the operation [5]. Although we debate the virtues of lymphadenectomy versus lymph node biopsy at the time of lung resection and the value of a sentinel node technique, the realities are that only the minority of surgeons are adequately sampling any mediastinal lymph nodes. Only those nodes clinging to the lobectomy or pneumonectomy specimen are typically available to the pathologist for analysis. This is below my personal standard of care, and I suggest it should it below the standards acceptable to the thoracic surgery community as represented by its societies and the Board of Thoracic Surgery. Retrieval and identification of lymph nodes from all appropriate ipsilateral stations must be a required metric in all quality assessments of lung cancer surgery. Then the debate of excision versus sampling and assessment of a radio-guided sentinel node technique can continue with a minimum performance standard having been established.
In summary, this current article suggests promise for the radio-guided sentinel lymph node technique with potential for use intraoperatively, but immediate application for postoperative, pathologic staging by focusing the pathologist on the lymph node or nodes most at risk for harboring micrometastases that can then be evaluated in the appropriate scientific fashion. But the pathologist can only examine nodes that are excised and submitted. Therefore no metastatic nodes is "good nodes," but no nodes available for examination is the opposite.
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