Ann Thorac Surg 2006;81:292-297
© 2006 The Society of Thoracic Surgeons
Original article: General thoracic
Prognostic Significance of Metastasis to the Highest Mediastinal Lymph Node in Nonsmall Cell Lung Cancer
Yukinori Sakao, MD, PhD
*
,
Hideaki Miyamoto, MD, PhD,
Akio Yamazaki, MD, PhD,
Tsumin Oh, MD,
Ryuta Fukai, MD,
Kazu Shiomi, MD,
Yuichi Saito, MD
Department of General Thoracic Surgery, Juntendo University School of Medicine, Tokyo, Japan
Accepted for publication June 24, 2005.
* Address correspondence to Dr Sakao, Department of General Thoracic Surgery, Juntendo University School of Medicine, 2-1-1 Hongo, Bunkyo-ku, Tokyo 113-8421, Japan (Email: sakao{at}med.juntendo.ac.jp).
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Abstract
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BACKGROUND: We have tried to clarify the prognostic significance of metastasis to the highest mediastinal (HM) lymph node in patients with N2 lung cancer who underwent complete dissection of superior mediastinal (including HM) lymph nodes.
METHODS: This study analyzed 53 patients with N2 nonsmall cell lung cancer who underwent surgical procedures such as lobectomy plus hilar and mediastinal node dissection (T4, neoadjuvant therapy cases were excluded). For patients whose cancer was in the left lung, we performed surgery through the median sternotomy in order to dissect superior mediastinal nodes. The clinicopathologic records of the patients were examined for prognostic factors such as age, sex, side, histology, tumor location, tumor size, clinical node (cN) number, preoperative serum carcinoembryonic antigen level, number of metastatic stations, and HM lymph node involvement.
RESULTS: A univariate analysis showed that tumor size (T1/T2-3), cN factor (cN1-2/cN0), N2 level (multiple/single), and metastasis to the HM node were significant prognostic factors. In the multivariate analysis, metastasis to the HM lymph node remained a significant prognostic factor (p = 0.026). The 3-year survival rates were 52% in patients without metastasis to the HM lymph node and 21% in patients with metastasis to the HM lymph node (p < 0.001). Furthermore, when HM nodal involvement was absent, the 5-year survival rate was 33% even in patients with multilevel N2 status, 45% in patients with cN1-2 status, and 47% in patients with pT2-3 tumor status.
CONCLUSIONS: Highest mediastinal lymph node involvement is prognostic of highly advanced N2 disease resulting in poor outcome. The results also suggest that patients with no involvement of the HM lymph node can experience acceptable postoperative outcomes even if they have multilevel N2 status, positive cN status, or T2-3 tumor status.
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Introduction
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The presence of metastasis to the highest mediastinal (HM) lymph node in patients with N2 lung cancer has been defined as a finding of incomplete resection [1, 2]. However, previous studies regarding postoperative prognosis in such patients have not clarified the impact of HM lymph node involvement [3–6]. Recent studies have shown that positive HM nodal status was not related to prognosis after surgery [7]. Thus, the impact of HM lymph node involvement as a prognostic factor in N2 lung cancer is undefined.
In this retrospective study, we have tried to clarify the prognostic importance of HM lymph node involvement in patients with N2 lung cancer who underwent complete dissection of the HM lymph node.
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Patients and Methods
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Between 1996 and 2003, 433 patients underwent surgical resection of primary lung cancer within our department. Of those, 82 patients were diagnosed as having mediastinal lymph node involvement by pathological examination. The mediastinal nodal status (HM lymph node) was assessed according to the system of Mountain and Dresler [9] and Naruke and coworkers [10]. All the 82 patients underwent ND2a dissection (for upper lobe: superior and subcarinal nodes; for middle or lower lobes: superior and inferior mediastinal nodes), including complete superior mediastinal (highest mediastinal, upper paratracheal, and lower paratracheal) nodal dissection. The HM lymph node is defined as nodes lying above a horizontal line at the upper rim of the bracheocephalic (left innominate) vein where it ascends to the left, crossing in front of the trachea at its midline [9]. For patients with cancer in the left lung, we performed surgery through a median sternotomy in order to completely dissect superior mediastinal nodes according to Hata's method [11, 12]. Briefly, the anterior mediastinal tissue is removed after the median sternotomy. The lymph nodes around the right and left recurrent laryngeal nerves directly under the thyroid gland, which is the upper limit of mediastinal dissection, and then a series of lymph nodes on the bilateral sides along the trachea were dissected (Fig 1) [11, 14]. When it was difficult to distinguish the ipsilateral lymph nodes from contralateral lymph nodes in the dissected tissue, the lymph nodes around the trachea were included in this study (as N2) for left lung cancer.
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Fig 1. Intraoperative view of mediastinum. After dissection of superior mediastinal lymph nodes through a median sternotomy, the ascending aorta was retracted to the left side. The boxed area shows the anatomical location of highest mediastinal lymph nodes. (BCA = brachiocephalic artery; BCV = brachiocephalic vein; laryngeal N = recurrent laryngeal nerve [taped]; Lt = left; PA = pulmonary artery; Rt = right; Tr = trachea; vagal N = vagal nerve [taped].)
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After exclusion of patients with T4 tumor status, and those who received neoadjuvant therapy, 53 patients remained and were analyzed in this study. None of the 53 patients received any adjuvant therapy.
The group comprised 15 female and 38 male patients, with ages ranging from 28 to 80 years (median age, 63). Preoperative staging was performed according to the TNM classification system of the International Union Against Cancer [8] using chest computed tomography (CT), abdominal CT or ultrasonography, brain CT or magnetic resonance imaging, and bone scanning in all patients. Mediastinal and hilar lymph node status was assessed as positive if the chest CT showed that the shorter axis of any node was larger than 1.0 cm. Mediastinoscopy and positron emission tomography (PET) have not been performed routinely in this series. Scalen node biopsy was performed in patients with suspicions of N3 (neck) in physical examination. When N3 (neck) was confirmed pathologically, the patients did not undergo surgery. The follow-up duration ranged from 12 to 96 months (median, 56).
The clinicopathological records of each patient were examined for prognostic factors such as age, sex, right or left side cancer, histology, tumor location (upper or lower), tumor size, cN number, preoperative serum carcinoembryonic antigen level, metastatic stations (single or multiple locations) according to Naruke's system [10], and distribution of metastatic nodes. Patient characteristics are summarized in Table 1.
Statistical Analysis
The duration of survival was defined as the interval between the day of surgery and the date of death by any cause or the last follow-up date. Survival rates were calculated using the Kaplan-Meier method, and univariate analyses were performed using the log-rank test or the logistic regression procedure test. Multivariate analyses were performed by means of the Cox proportional hazards model using Stat View J 5.0 (SAS Institute, Cary, North Carolina) in variables with p value of less than 0.05 in univariate analyses. A pvalue of less than 0.05 was treated as significant.
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Results
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Survival Rate
The postoperative prognosis for 53 patients with N2 (without T4) lung cancer is shown in Figure 2. The overall survival rate at 5 years was 41%.
Incidence of Highest Mediastinal Lymph Node Involvement
Highest mediastinal lymph node involvement according to the primary site is shown in Table 2. The incidence of HM involvement was unrelated to location of the tumor in the right lobe (8 of 37) versus the left lobe (6 of 16), and the upper lobe (8 of 33) versus the lower lobe (6 of 16; p = 0.31 and p = 0.50, respectively).
Univariate and Multivariate Analyses of Prognostic Factors
A univariate analysis using the variables listed in Table 3
showed that pathologic tumor (pT) size (pT1/pT2-3), cN factor (cN1-2/cN0), N2 level (multiple/single), and metastasis to the HM lymph node were significant prognostic factors. Skip N2 exhibited a trend toward being a significant prognostic factor. In the multivariate analysis (using variables that had a p value less than 0.05 in the univariate analysis), metastasis to the HM lymph node was a significant prognostic factor (Table 4).
Survival Rate According to Involvement of Highest Mediastinal Lymph Node
Postoperative survival in patients with N2 according to HM lymph node involvement is shown in Figure 3. There was a significant (p < 0.001) difference between the two groups; the 3-year survival rates were 52% for patients without metastasis to the highest mediastinal node, and 21% for patients with metastasis to the highest mediastinal node. Highest mediastinal involvement was a prognostic factor even in patients who had other indicators of poor prognosis identified in the univariate analysis. For example, for patients with no HM lymph node involvement, the 5-year survival rate was 33% even for those with multilevel N2, 45% in cN(+), and 47% in pT2-3 (Fig 4A, B, and C).
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Fig 3. The 5-year survival rate in patients diagnosed with N2 lung cancer depending on involvement of the highest mediastinal (HM) lymph node.
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Fig 4. (A) The 5-year survival rate in patients diagnosed with N2 lung cancer depended on highest mediastinal (HM) lymph node involvement and involved station levels. (B) The 5-year survival rate in patients diagnosed with N2 lung cancer depended on HM lymph node involvement and pT status. (C) The 5-year survival rate in patients diagnosed with N2 lung cancer depended on HM lymph node involvement and CN status. (CN = clinical node; meta = metastasis; pT = tumor pathology.)
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Association Between Highest Mediastinal Lymph Node Involvement and Other Prognostic Factors
A 
2 analysis using the variables listed in Table 5
showed that cN factor (cN1-2/cN0), N2 level (multiple/single), and skip N2 were associated with HM lymph node metastasis (p = 0.026, p < 0.0001, p = 0.023, respectively).
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Comment
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Our results indicate that HM lymph node involvement was one of the most important prognostic factors for poor outcome after surgery in patients with N2 disease. Several factors such as cN factor, N2 level, tumor size, tumor location, and skip N2 have been reported as being important postoperative prognostic factors in N2 patients [3–6, 9, 10]. However, the impact of the location of involved mediastinal nodes (stations), in particular HM node involvement, has been defined as a finding of incomplete resection [1, 2], the prognostic significance of this factor has been unclear [7]. The present study showed that cN status (cN0 versus cN1-2), involvement of multiple lymph node levels, T status (T1 versus T2-3), as well as HM nodal involvement were significant (p < 0.05) prognostic factors in a univariate analysis. Tumor location was not a significant prognostic factor in this study. Furthermore, multivariate analysis confirmed that HM nodal involvement was a significant prognostic factor. In the N2 patients, the 3-year and 5-year survival rates were 35% and 0% (no patient lived beyond 40 months) in those with HM lymph node involvement, but 60% and 55% in those without HM lymph node involvement (p < 0.001).
The 5-year survival rate was 35% when HM lymph node was not involved, even for patients with multilevel N2. However, the 3-year survival was 20% and the 5-year survival was 0% for patients with multilevel N2 and HM lymph node involvement. Similarly, even in cN positive or T2-3 patients, the 5-year survival rate was greater than 40% when the HM lymph node was not involved. In contrast, when the HM lymph node was involved in otherwise similar patients, the prognosis was very poor (0% at 5-year survival; Fig 4A through C). Thus, HM nodal involvement was a very strong prognostic factor for poor outcome in N2 patients. Highest mediastinal lymph node involvement was also associated with cN factor (cN1-2), N2 level (multiple station metastases), and skip N2 (nonskip N2). These factors have been recognized as indicators of more advanced N2 resulting in poor outcome [3–6]. According to these results, HM lymph node involvement can be recognized as a simple and reliable finding that indicates highly advanced N2 lung cancer. Without HM involvement, even among patients with multilevel N2 nodal status, with positive cN status, or with T2-3 tumor status, surgical resection can lead to acceptable postoperative outcomes (at least 30% 5-year survival rate).
It is difficult to perform complete dissection of the superior mediastinal nodes through the left thoracotomy used for resection of tumor in the left lung; it is comparatively easier with a right thoracotomy. Since the favorable postoperative outcome in N2/N3 lung cancer reported by Hata and colleagues [11], we have performed a median sternotomy in patients with lung cancer in the left lobe in order to completely dissect the superior mediastinal nodes. The Japan Clinical Oncology Group reported the incidence of HM lymph node involvement in patients with multilevel N2. They reported that patients who received the standard ND2a dissection through the thoracotomy exhibited HM involvement in 46% of cases (52 of 113) of right lung cancer, but in only 3.8% of cases (3 of 80) of left lung cancer [4]. In the present study, there was no difference in the incidence of HM lymph node involvement comparing patients with right and left side tumors (Table 2). The difference in the incidence of HM involvement between right and left lung cancer reported in the previous study [4] supports the idea that HM node dissection cannot be performed adequately through a left thoracotomy. If the impact of HM metastasis were analyzed using data only from patients with right lung cancer, results similar to those of the present study may be demonstrated. However, we are unaware of such an analysis in the literature. In our study, the prognostic importance of HM lymph node involvement was independent of whether the primary tumor was in the left or right lung (data not shown).
Hata and coworkers [13] used scintigraphy in healthy volunteers to show that the main lymphatic route from any pulmonary lobe was connected with both sides of the supraclavicular lymph nodes through the superior mediastinal nodes. The HM lymph node is the nearest mediastinal station that connects with the venous angle (supraclavicular lymph nodes), which is the entrance to the major systemic blood vessels. Furthermore, Miyamoto and associates [14] reported that 8 of 10 patients with HM lymph node involvement (cN0, 2 cases, and cN2, 8 cases) had neck (including supraclavicular) lymph node metastases; these patients exhibited very poor outcome in an analysis of patients who underwent neck and mediastinal dissection. Thus, HM lymph node involvement implies the presence of metastases to the neck lymph nodes or spreading of the tumor cells into the blood stream through the supraclavicular lymph nodes.
Thus, patients with HM lymph node metastasis must be candidates for multimodal therapy due to its poor outcome after surgery, and recent diagnostic modality such as positron emission tomography may be able to detect patients with HM involvement without surgery.
Limitations of this study include its being a retrospective one and the small sample size.
In summary, our results suggest that metastasis to HM lymph node implies incomplete resection, and should be considered prognostic of poor outcome after surgery. Patients with such findings should be classified as having highly advanced N2 disease. The results also suggest that patients with no involvement of the HM lymph node can experience acceptable postoperative outcomes (at least 30% 5-year survival rate) even if they have multilevel N2 status, positive cN status, or pT2-3 tumor status.
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Acknowledgments
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We thank Enjo Hata, Chief, Surgical Department of Respiratory Center, Mitsui Memorial Hospital, and Edmund J Miller, Chief, Surgical Immunology, North Shore University Hospital, for critical reviews.
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Abstract
Introduction
