Caudal border of level 2R in the new international lymph node map for lung cancer.

To the Editor: Recently, the International Association for the Study of Lung Cancer (IASLC) proposed a new lymph node map1 that was published in “Staging Manual in Thoracic Oncology.”2 This lymph node map was created by the integration of information obtained worldwide, and the members of the IASLC staging committee have worked diligently toward establishing it. It is essential for significant analysis and revision toward the next eighth edition of tumor, node, metastasis (TNM) classification that we have a good understanding of this map and endeavor to operate the seventh edition of TNM classification properly. However, for the proper operation of this map, we need to correctly identify the lower border of level 2R. This border is defined as “the intersection of the caudal margin of the innominate vein with the trachea.” Unfortunately, by referring the manual,2 we could not identify the lower border of level 2R. Initially, we literally interpreted this definition and drew line “a,” (Figure 1A), which was obtained by marking the line of overlap of the caudal margin of the innominate vein and the trachea. After studying the figures in the article1 and the manual,2 we think that the border should be horizontal for the convenience of computed tomographybased diagnosis and staging. From the definition of line “a,” it seems that this line will mostly be diagonal; this will make computed tomography-based diagnosis difficult as mentioned before. Therefore, we think that two more borders could be drawn in Figure 1A as follows: (1) line “b” can be drawn horizontally from the intersection of the caudal margin of the innominate vein to the right margin of the trachea and (2) line “c” can be drawn horizontally from the caudal point of confluence of the innominate vein and the superior vena cava (SVC). However, there would be drawbacks to using both these lines too, even though they are horizontal. In the case of line “b,” the required intersection point through which this line passes would be absent in cases where the left margin of the SVC overlaps with the trachea. For line “c,” there would be some difficulties in identifying the point of confluence of the innominate vein with the SVC. These difficulties can be overcome if it is clarified whether the lymph node illustrated in Figure 1B is level 2R or level 4R. We hope the IASLC will help us bridge the information gap between the sixth and seventh editions of the TNM classification for lung cancer.