Lymph Node Dissection for Lung Cancer



Lymph Node Dissection for Lung Cancer


Hisao Asamura



Historical Note

The role of mediastinal/hilar lymph node dissection (LND) in the staging and treatment of lung cancer remains controversial. In particular, the prognostic significance of hilar/mediastinal LND has been one of the most important issues in thoracic surgery, although LND was adopted early as a routine procedure in the evolution of lung cancer surgery. In the 1930s, pioneer surgeons such as Nissen, Graham, and Overholt demonstrated that pneumonectomy could be performed for lung cancer and that this procedure could be expected to provide a cure. Based on the observation that locoregional lymph nodes were often involved by the tumor, hilar/mediastinal LND was proposed in combination with pneumonectomy in the 1940s by Allison1 and Brock.2

In 1951, Cahan, at Memorial Sloan-Kettering Cancer Center in New York City, published an article entitled “Radical pneumonectomy” and proposed for the first time the concept of radical resection for lung cancer.3 He described an operative procedure with resection of the entire lung (pneumonectomy) and locoregional lymph nodes (LND) in an en bloc manner, emphasizing the importance of en bloc resection of mediastinal lymph nodes in conjunction with pneumonectomy. Nine years later, he published another article entitled “Radical lobectomy,” a surgical procedure whereby one or two lobes of the lung were excised in a block dissection with their regional hilar and mediastinal lymphatics.4 He also showed that lobectomy could be chosen as an alternative to pneumonectomy in the surgical management of lung cancer without worsening the prognosis. The extent of LND was clearly defined according to the primary site (lobe) of the disease. Since this landmark article, hilar/mediastinal LND has been adopted as part of the standard technique for malignant disease of the lung, although the therapeutic effect (if any) remained unclear.

In the 1990s, the pattern of lymphatic spread and its relation to prognosis were studied in detail, and the lobe-specific extent of LND has been proposed.5,6,7 Furthermore, owing to the availability of low-dose computed tomography (CT) screening programs and the improved quality of the CT scan itself, fainter and smaller tumors are now being found. For such early tumors, the extent not only of parenchymal resection but also that of LND needs to be modified. Such studies are under way.


Lymph Node Dissection (LND) and Lymph Node Sampling (LNS): Definitions

As surgical techniques or concepts, LND and LNS must be clearly distinguished. When the term LND is used, all of the lymph nodes in the targeted compartment must be completely removed, as a block, together with surrounding adipose tissue. This means that all of the lymph nodes in the compartment are removed with connecting lymphatic vessels to ensure the complete clearance of latent cancer cells from the lymphatic system. Here, LND is performed to achieve both accurate staging and improved local control, although the latter has not yet been proven. In contrast, LNS refers to the removal of individual lymph nodes without any surrounding tissue, guided by preoperative or intraoperative findings thought to be representative. The primary purpose of this procedure is tissue sampling and biopsy. Accordingly, when only the term sampling is used, it means that only those lymph nodes that are obviously abnormal are removed. In the guidelines for intraoperative lymph node staging, the European Society for Thoracic Surgeons (ESTS) has defined the method of lymph node assessment as “selective lymph node biopsy,” “sampling,” and “systematic LND.”8 According to this recommendation, one or more suspicious lymph nodes are biopsied in “selective lymph node biopsy,” and LNS and LND are defined as described above.

Descriptors such as systematic, selective, and extended are sometimes used in combination with the terms of LND and LNS. Systematic LNS/LND is used when all of the designated lymph node stations specific to the location of the primary tumor are routinely covered. Extended and selective LND refer to the extent of lymph node dissection. For oncologic or physical reasons specific to the patients, the extent of LND is minimized in selective LND. Extended LND usually means that the extent of lymph node dissection is widened beyond the routine anatomic stations. The contralateral mediastinal LND via median sternotomy is an example of extended LND, in which the lymph nodes in the N3 region
are also removed with the aim of achieving the better local control.9


The Lymph Node Map

The nomenclature of lymph node sites has developed through the topographic analysis of lymph node spread in lung cancer. Naruke and colleagues10 published a landmark article in 1978 in which they proposed a novel lymph node map. The lymph node sites are classified as “stations” based on the anatomic structures of the mediastinum and bronchial tree. Mediastinal node stations are assigned numbers from 1 to 9 (single-digit numbers) and hilar/interlobar/intrapulmonary stations are assigned numbers from 10 to 14 (two-digit numbers). The most important contribution of this system is that it enabled the uniform description of lymph node status. In 1981, the American Thoracic Society promulgated a lymph node map (the “ATS map”) and defined lymph node levels that were different from those of Naruke’s original map.11 However, the basic rule of using single-digit numbers for mediastinal levels and two-digit numbers for hilar/interlobar/intralobar levels was maintained. In 1997, Mountain and Dresler further revised the ATS map to reconcile the difference between the Japanese–Naruke and the ATS maps.12 In this new ATS map, the boundary between mediastinal (N2 nodes) and hilar (N1 nodes) was defined as the mediastinal pleural reflection.

The most serious difference between the Japanese–Naruke and ATS–Mountain maps is the definition of lymph node sites around the mainstem bronchus. This issue is closely related to the definition of nodal status as N1 or N2.13 In the ATS–Mountain map, the boundary between N1 and N2 stations is the reflection of the mediastinal pleura, and station (level) 10 was pushed away distally. While level 10 in the Japanese–Naruke map designates the lymph nodes around the mainstem bronchus, level 10 in the ATS-Mountain map designates the proximal lobar bronchus. In contrast, level 10 in the Japanese–Naruke map is classified as level 4 in the ATS map. Accordingly, metastasis to the lymph nodes around the mainstem bronchus might be classified as N2 by the ATS–Mountain map or as N1 by the Japanese–Naruke map.

The present sixth edition of the TNM staging system of the Union Internationale Contre le Cancer (UICC) for lung cancer14 is being revised by the joint task force of the UICC and International Association for the Study of Lung Cancer (IASLC). For this purpose, the IASLC initiated the IASLC Staging Project early, before the actual revision. In this registry study, 100,809 patients from all continents were registered. Proposed changes for T, M, and stage grouping by the IASLC have already been published,15 and this is to be approved by the UICC in 2008. The creation of a new international lymph node map is one of the goals of the IASLC staging project, and this effort is under way. The staging committee of IASLC has reached the final proposal of new lymph node map in 2008, and by the authorization of UICC and AJCC (American Joint Committee on Cancer), the new lymph node map is to be launched early in 2009. This new map has revised the anatomical definition of each lymph node level, and rearranged the numbering for newly defined levels. Best efforts were also taken to describe the clear-cut boundary between neighboring levels, especially between N1 and N2 levels. Beside the level, the new concept of lymph node location, “zone”, is also introduced. The future description about the lymph node status will be based on this new lymph node map world-wide, the discrepancy of nodal evaluation because of the lymph node map will disappear.


Purpose and Benefit of Hilar/Mediastinal Lnd

The goals of hilar/mediastinal LND are accurate intraoperative staging and the improvement of survival through better local control.

A more accurate evaluation of the stage could be expected by the pathologic examination of the dissected lymph nodes. Some data clearly show that systematic LNS or LND improves intraoperative staging in contrast to selective lymph node sampling, especially in the detection of multilevel N2 disease.16,17 In a well-known study conducted by the Lung Cancer Study Group, lobectomy and limited resection were compared in clinical stage I (T1N0) non-small-cell lung cancer <3 cm in diameter.18 Survival was improved in the lobectomy group, but the difference was of borderline statistical significance. Interestingly, even though the study population was limited to those with clinical T1N0 disease without lymph node involvement, 25% of the patients were found to have positive mediastinal lymph nodes. In addition to the principal finding of better survival in patients who underwent lobectomy, this high percentage of positive lymph node metastases also provided a rationale for performing lobectomy with complete LND, even for T1N0 non-small-cell lung cancer. More recently, several large-scale randomized trials have shown that postoperative adjuvant chemotherapy might be able to improve the survival after surgery for non-small-cell lung cancer.19,20,21,22 According to the results of these studies, a favorable outcome could be achieved for patients with lymph node involvement compared with those without lymph node involvement.19 Thus accurate staging by surgical exploration of the lymph nodes enables the selection of better candidates for adjuvant postoperative chemotherapy. These are definitive benefits of accurate staging.

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Jun 25, 2016 | Posted by in RESPIRATORY | Comments Off on Lymph Node Dissection for Lung Cancer

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