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Ann Thorac Surg 2000;70:389-390
© 2000 The Society of Thoracic Surgeons
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Discussion |
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 Top Discussion |
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Just as some of us were thinking that nothing really new was happening in lung cancer surgery, at least in the operating room, Dr Liptay and his colleagues bring us a new gadget and radioisotope and potentially more insight into the staging of non–small cell lung cancer. The true sentinel lymph node is the lymph node most likely to harbor metastatic disease if regional nodal metastasis is present. Doctor Liptay and his colleagues have demonstrated elegantly that the lymph node they identify as the sentinel node was metastatic roughly one third of the time with an accuracy of 95%. The success of sentinel node technique depends on identifying the first lymph node draining the primary tumor. The sentinel node should be the first draining node and the only hot node if the mapping procedure is performed timely after injection. In the case of breast cancer, as time goes on, the isotope material flows further up the chain of nodes and additional nodes become hot; not only that, the hottest node is not always the sentinel node.
Potential benefits of this modality include clarification of the concept of skip metastasis and the decrease in morbidity of the lymphadenectomy, although in our database in Rochester, lymphadenectomy accounts for only less than 3% of significant morbidity after thoracotomy for lung cancer. Perhaps the greatest benefit of the sentinel node technique is to allow for a more thorough pathologic examination of the sentinel node, because the false-negative rate of frozen section can be as high as 10% in some institutions. A final benefit is the potential to improve staging and survival.
Potential disadvantages include radiation safety regulation, of course; the learning curve; the use of gamma detection instrumentation; and the possible allergic reaction to the colloid used. The technique is an interdisciplinary process, including the pathologist and the radiation doctor. The procedure is complicated by the preparation of the radiocolloid; the "shining through" effect that Dr Liptay mentioned from the primary tumor, which might overshadow the sentinel node count; and, finally, the false-negative nodes because of obstructive lymphatics and rerouting of the drainage and the fatty infiltration of the lymph node that is well known in breast cancer patients and older patients.
We do not know yet if all this will matter in the end. So far no survival benefit from lymphadenectomy has been demonstrated through a prospective randomized trial. The benefit of complete lymphadenectomy versus sampling hopefully will be clarified with Dr Keller’s presentation this morning and other trials such as the American College of Surgeons lymph node dissection. If sampling prevails, intraoperative radioisotope sentinel lymph node mapping might become relevant. If total lymphadenectomy is proved to be superior, mapping will not accomplish much for the surgeon in the operating room.
If it ever comes to common use, lymphatic mapping with colloid agents will not realize its full potential until it is standardized. Potential variations include the nature of the colloid used, the amount injected, the distance between the lymph node and the primary tumor, the size of the primary tumor, and the arbitrary definition of what radioactive count should constitute the sentinel node, what is the correct ex vivo node to background ratio count, and the correct ex vivo node to sentinel node ratio count.
Doctor Liptay, you and your colleagues have shown that radionucleide mapping for lung cancer is feasible and accurate with low morbidity and no mortality. It is a good start. Further studies are needed and time will tell if all this will have an impact on the survival of our lung cancer patients.
I have three questions. Did you see a difference in time to identification of sentinel node between upper and lower lobe tumors? In the breast cancer and melanoma experience there is a suggestion that successful mapping is directly related to the surgeon’s experience and there is a recommendation of 30 to 50 cases to achieve an acceptable level of competence. Did you feel that you had to ascend a learning curve, and if yes, how many cases would you think a surgeon would have to handle to become competent to carry out this procedure?
One of the objectives you had in your article and your presentation today was to determine if the operative time would be longer. There is no information about the operative time specifically in the manuscript or your presentation and you mention no direct complication. Do you actually know by how much the mean operative time was extended since you had at least 1 patient for whom it took 1.5 hours to determine the migration time?
I enjoyed reading your article and your presentation and I thank the Society for the opportunity of discussing this excellent paper.
Dr. John R. Benfield (Los Angeles, CA): This is an important paper. One can say that much of the progress that has been made in selecting patients for lung cancer operations and induction therapy is based on accurate staging. Nowadays we often, use fine-needle aspiration preoperatively to obtain a secure diagnosis. My question is, what are the barriers to preoperative injection of technetium and then extending the technique to a preoperative scanning technique thus trying to find the sentinel node before one is actually at the operating table?
Dr. Liptay: Thank you, Dr Deschamps and Dr Benfield, for your comments. Dr Deschamps, I will try to take your questions first.
We did not notice any difference in the time of migration required to identify a sentinel node between upper and lower lobe tumors. That being said, as you are aware, our sample size was small, which leads into the next question about a learning curve. For 4 of the first 12 patients we did not have successful migration of radioisotope. All of them had less than 30 minutes’ time before we attempted to assess the nodes. Thereafter, we used 30 minutes as a minimum before probing the nodes for migration and observed much more reliable results.
I would say the learning curve for this procedure is still evolving. As far as specifically how many cases are required before obtaining reliable results, I think certainly a surgeon who is familiar with performing anatomic resections with mediastinal node dissections should not have much difficulty with handling the probe and measuring the radioactivity counts. The procedure is not that difficult. That being said, I think probably 10 to 20 cases would be reasonable before embarking on meaningful data in what I hope is a multi-institutional trial to test this technique.
As for the additional operative time required, we did not measure the time associated with the sentinel node technique specifically. The node mapping procedure adds all of about 10 minutes total. That is really all the added time it takes. If you were not planning on carrying out a mediastinal node dissection, which we perform routinely, you could count that extra 20 minutes as adding to the operative time.
The specific case for which we reported a migration time of 170 minutes was actually a Pancoast resection that had an en bloc first through fourth rib resection along with the lobectomy and mediastinal node dissection. As you also mentioned about the "shining through" effect of the tumor, we cannot really obtain an accurate measurement of the sentinel nodes until the tumor is out of the chest and the lymph nodes are separated because of the spatial closeness of the tumor that carries the most radioactivity.
Regarding your question, Dr Benfield, we initially had planned on injecting these tumors the night before surgery, as is the protocol for our breast cancer patients. One of the barriers to doing that certainly is subjecting the patient to a separate procedure if a needle biopsy was not planned. Likewise, the risk of pneumothorax, bleeding, and potential seeding of tumor cells in the chest wall during that procedure are also considerations. Fortunately, because of the rich vascular and lymphatic supplies of the lung compared with the breast or skin in melanoma the transit time of the radioisotope is rapid enough to allow intraoperative injection. Although I have no data to support this statement, I would suspect that preoperative injection might lead to multiple radioactive lymph nodes with the added migration time potentially making the readings difficult to interpret.
Related Article
Ann. Thorac. Surg. 2000 70: 384-389.
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