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Ann Thorac Surg 2001;72:1440
© 2001 The Society of Thoracic Surgeons
a Division of Thoracic Surgery, National Cancer Center Hospital, 1-1, Tsukiji 5-chome, Chuo-ku, Tokyo 104-0045, Japan
e-mail: hasamura{at}gan2.ncc.go.jp
To the Editor
I appreciate the interest of Dr Riquet and colleagues in the study on the boundary between N1 and N2 lymph node stations in lung cancer [1]. Because there are different maps of the lymph node stations, some of the nodes around the main bronchus (close to the pulmonary hilum) can be classified either as N1 or as N2. Because nodal status is one of the important factors in the TNM staging system, an equivocal nodal description is directly related to the equivocal (inaccurate) stage of the patient with lung cancer.
On the basis of the superimposed survival curves of single-node and single-station N2 disease and N1 No. 10 disease, Dr Riquet and associates proposed a pathological N classification with three categories: "N0 and intralobar N1, extralobar and single anatomic chain N2, and two or more chains N2." In terms of the prognosis for patients having resection, their proposal may best reflect the clinical outcome and is attractive especially to surgeons. However, this nodal categorization is based only on the information provided by surgical exploration and subsequent pathological evaluation of extirpated nodes. Even during the operation, it is difficult for surgeons to know exactly how many lymphatic chains are involved. Furthermore, the clinical (preoperative) and pathological (postoperative) description of each TNM factor should be basically the same. A TNM denominator must be simple and applicable to patients both preoperatively and postoperatively. In the preoperative setting, a distinction between "single anatomic chain N2" and "two or more chains N2" does not seem realistic.
To explain "skip" metastasis in lung cancer, Dr Riquet and colleagues stressed an anatomical reason based on embryological considerations involving the lymphatic pathways of the lung. The existence of the first lymph nodes in the mediastinum, not in the lung, is given as the cause of skip metastasis. Today, these nodes are called "sentinel nodes." Such an anatomical observation may be reflected in the categorization suggested by Dr Riquet and colleagues, which divides N2 disease into single-chain and multiple-chain N2 regardless of location of involved nodes. Indeed, skip metastasis occurs in or around 25% of N2 disease [2–5]. However, skip metastasis is found almost exclusively in adenocarcinoma, not in squamous cell carcinoma or in small cell carcinoma, as previous studies demonstrated [2, 3]. This indicates that the phenomenon of skip metastasis is not simply a matter of anatomical structure of the lymphatic pathway. Therefore, I am still careful in attaching importance to the number of lymphatic chains involved in nodal categorization.
Again, I really appreciate the concern of Dr Riquet and coauthors about nodal mapping in lung cancer. I emphasize that we surgeons and physicians must have a single universally used map for lymph node stations. Without such a map, there cannot be accurate TNM staging. Further discussion on a better lymph node map must continue from anatomical, therapeutic, and pathological viewpoints.
References
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