Evaluation of the significance of subcarinal lymph node dissection in stage IB non‑small cell lung cancer
- Authors:
- Published online on: May 16, 2023 https://doi.org/10.3892/mco.2023.2646
- Article Number: 50
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Copyright: © Wang et al. This is an open access article distributed under the terms of Creative Commons Attribution License.
Abstract
Introduction
Being the most prevalent type of malignant tumor, lung cancer has the highest cancer-related mortality worldwide with 2093876 new cases and 1761007 cases died of lung cancer in 2018(1). Non-small cell lung cancer (NSCLC) is the most common pathological type of lung cancer, accounting for ~85% of lung cancer cases (2). Widespread application of chest CT in physical examination facilitates diagnosis of early-stage NSCLC. Currently, surgery is the first-line treatment option for early-stage NSCLC (3). Lobectomy with systematic lymph node dissection (SLND) has been the standard surgical treatment for lung cancer for several years (4,5). However, there are new options for LND in early-stage NSCLC, among which lobe-specific selective LND (LSLND) is one of the most discussed surgical methods (6-9). Studies have confirmed that LSLND could shorten the operation time and decrease perioperative complications without affecting overall survival (OS) and disease-free survival rate of patients after surgery (8-10). In addition, some studies suggested that for early-stage NSCLC, lymph node sampling (LNS) achieves a prognosis similar to SLND (11,12). The subcarinal lymph node, also known as the #7 lymph node, has been regarded as an essential N2 lymph node in LND of lung cancer in the past and it was required to be removed in SLND. The extent of SLND involves the inclusion of subcarinal lymph nodes, while LSLND and LNS do not require mandatory subcarinal LND (8-10,12). There is still controversy about whether the subcarinal lymph nodes must be dissected in early-stage NSCLC. The present study focused on stage IB NSCLC and investigated if the subcarinal LND is necessary for stage IB NSCLC.
Materials and methods
Patient selection
Data were collected from patients with lung cancer who had surgery at Sun Yat-Sen University Cancer Center, Guangzhou, China between January 1999 and December 2009. The medical records and the follow-up system were evaluated for patient information, postoperative pathological information, surgical conditions and follow-up outcomes. The inclusion criteria were as follows: i) No neoadjuvant therapy; ii) patients treated with lobectomy and iii) postoperative pathological diagnosis was stage IB NSCLC, which was validated independently by two pathologists. The exclusion criteria were as follows: i) Patients who had preoperative chemotherapy or radiation; ii) patients with other types of tumor and iii) no detailed follow-up information. Finally, 597 patients (age range 19-85; male/female 425/172) were enrolled.
Follow-up
Follow-up began when patients underwent surgery and was performed every 3 months for the first 2 years, every 6 months between 3-5 years and annually after 5 years. The evaluation of the patient condition included routine blood, blood biochemistry, tumor marker, abdominal ultrasound and chest CT. Brain MRI was conducted to determine brain metastasis once per year . The patient survival and recurrence were recorded at each visit. All cases were followed up until January 2013.
Statistical analysis
The variables of the two groups were compared using χ2 or Fisher's exact (>20% of cells with expected frequency <5) test as appropriate. OS and recurrence-free survival (RFS) were calculated using the Kaplan-Meier method. For univariate and multivariate analysis, the Cox proportional hazard regression model was utilized. Variables with P<0.1 in univariate analysis were used in the multivariate analysis. P<0.05 was considered to indicate a statistically significant difference. Statistical analysis was performed with the R software (version 4.2.0; R-project.org/). The ‘matchit’ (version 4.4.0; cran.r-project.org/web/packages/MatchIt/vignettes/MatchIt.html) package was used for propensity score matching (PSM). The ‘survival’ (version 3.3-1 cran.r-project.org/package=survival) and ‘survminer’ (version 0.4.9 cran.r-project.org/web/packages/survminer/readme/README.html) packages were used to generate survival curves and forest plots. Due to crossover in the survival curves, the two-stage test was used to calculate the P-value using the R package TSHRC (cran.r-project.org/web/packages/TSHRC/index.html) (13). X-tile (version 3.6.1; Yale University, USA; medicine.yale.edu/lab/rimm/research/software/) was used to determine the optimal cutoff values for the number of resected lymph nodes.
Results
Baseline characteristics
The current study included a total of 597 patients with stage IB NSCLC. The baseline characteristics of the study cohort are shown in Table I. The majority of patients were male (71.2%) and 32.2% of the patients were >65 years of age. Among all the included cases, 58.3% had smoking history and 16.1% had family history of malignancy. In terms of postoperative pathology, patients with grades I + II accounted for 60.5%. The most common pathological types were adenocarcinoma (64.2%), followed by squamous cell carcinoma (33.5%), while the remaining 2.3% included large cell carcinoma, sarcomatoid carcinoma and mucoepidermoid carcinoma. The proportion of cases with visceral pleural invasion was 60%, while that of bronchial invasion was 25%. In addition, 54% of the patients had >12 lymph nodes resected, while 28.3% of the patients had ≥6 lymph node stations resected. Following surgery, ~16.1% of patients received adjuvant chemotherapy.
Among all the cases included in the present study, 185 patients did not undergo subcarinal lymph node resection, whereas 412 did. Table I shows statistically significant differences in bronchial invasion, resected lymph node stations and resected lymph node numbers between the two groups.
Prognostic factors for OS and RFS
Before PSM, prognostic factors were evaluated with Cox proportional hazards regression models. Table II shows univariate analysis for OS and RFS. Variables with P<0.1 were included in the multivariate analysis. Age, family history of cancer and the resected lymph nodes number were significant prognostic factors for OS (Fig. 1), whereas only age and resected lymph node number were significant prognostic factors for RFS (Fig. 2). Cox regression analysis of all included cases suggested that resection of subcarinal lymph nodes was not a prognostic factor for OS and RFS.
 | Table IIUnivariate analysis of overall survival and recurrence-free survival before propensity score matching. |
Survival analysis
To compare the effect of subcarinal lymph node resection on OS and RFS, 1:1 PSM was performed for all variables. A total of 252 cases, 146 for each group, were selected after PSM (Table I). χ2 indicated that all variables were not statistically different between the two groups. Fig. 3 shows the distribution of propensity scores before and after matching. A good match was obtained between the two groups. Fig. 4 shows OS and RFS curves stratified with or without subcarinal lymph node resection before and after PSM. All four survival curves were not statistically significant, indicating that resection of subcarinal lymph nodes was not associated with OS and RFS.
Discussion
For LND in NSCLC, SLND (including subcarinal LND) has been the gold standard surgical treatment (14-16). However, with the increase in number of patients undergoing surgery for early-stage NSCLC (10), research has focused on new surgical approaches to LND in early-stage lung cancer. Among them, LSLND and LNS have been proposed by studies for the treatment of early-stage NSCLC (9,10,17,18). However, these LND methods do not emphasize the need to remove subcarinal lymph nodes. To explore the effect of subcarinal lymph node resection on prognosis in early-stage NSCLC, a total of 597 patients with stage IB NSCLC were included in the present study. Cox regression was used to investigate the prognostic factors and resection of the subcarinal lymph node did not affect OS and RFS. To decrease the influence of bias and confounding variables, survival analysis was performed after PSM, which suggested that the resection of subcarinal lymph nodes was not associated with OS and RFS.
International Association for the Study of Lung Cancer proposed the concept of SLND (19,20). In 2006, the European Society of Thoracic Surgeons guidelines defined the extent of resection in SLND as removal of ≥6 stations of lymph nodes, including >3 stations of mediastinal lymph nodes on the same side and the subcarinal lymph nodes (#7 lymph nodes) (14). Studies have found that SLND could improve the survival of patients with advanced NSCLC (12,21-23). SLND may increase surgical complications such as lymphatic fistula, recurrent laryngeal nerve injury, surgical blood loss and prolonged hospitalization (19); however, necessity of SLND remains controversial for early-stage NSCLC (24-26). For early NSCLC, several studies have suggested that LSLND and LNS achieve the same therapeutic effect as SLND (6,8,10-12,27). LSLND is defined as the removal of specific mediastinal and hilar lymph nodes according to the lobe of the tumor (9). LNS is defined as the resection of abnormal lymph nodes found preoperatively and intraoperatively (28). Neither of these two methods of LND for early-stage NSCLC require dissection of subcarinal lymph nodes and, according to the present findings, LNS and LSLND achieve the same therapeutic effect as SLND. The present study found that for stage IB NSCLC, there was no association between subcarinal lymph node dissection and OS or RFS. These results were consistent with the aforementioned previous findings on early-stage NSCLC.
Since the subcarinal lymph nodes are adjacent to the carina, esophagus and vagus nerve, these structures are prone to damage during dissection. Therefore, for early-stage NSCLC, surgeons may choose not to remove subcarinal lymph nodes. According to previous studies and the present study, the absence of subcarinal LND for early-stage lung cancer has no significant effect on OS and RFS. In summary, for early-stage NSCLC, not dissecting the subcarinal lymph nodes can decrease potential surgical damage, speed up surgery time and enable patients to recover faster (18,24,28). However, SLND could allow more accurate staging and provide an opportunity for postoperative adjuvant therapy (11,29). Therefore, SLND (including resection of subcarinal lymph nodes) may be recommended in patients who are considered at risk of lymph node metastasis in preoperative examination.
The present analysis suggested that subcarinal lymph node resection was not associated with OS or RFS. It could also be concluded that number of resected lymph node stations was not associated with OS or RFS. However, the number of resected lymph nodes in the multivariate analysis was a statistically significant prognostic factor for OS and RFS., while the resection of subcarinal lymph nodes and the resected lymph node stations were not statistically significant. These results indicated that for stage IB NSCLC, the number of dissected lymph nodes may be more meaningful in terms of improving prognosis than resection of the subcarinal lymph nodes and number of lymph node stations. Previous studies on NSCLC have suggested that this view remains controversial and needs to be confirmed by more studies in the future (30-32). If this conclusion is established, it will challenge the current principle of LND in lung cancer.
The current study had limitations. Firstly, this was a single-center retrospective study and multi-center prospective studies are needed to confirm the present conclusions. Secondly, this study enrolled 597 patients; this relatively small sample size could lead to bias. Due to the small sample size, no further subgroup analysis was performed for different pathological subtypes of NSCLC. Finally, the enrolled population of this study included only patients with postoperative pathologically confirmed stage IB; it is difficult to obtain the accurate pathological staging of patients before surgery. Therefore, the conclusions of this study have limitations in their future clinical application.
For stage IB NSCLC, there was no statistically significant association between resection of the subcarinal lymph node and patient survival. Subcarinal lymph node resection in surgery of stage IB NSCLC may be considered optional.
Acknowledgements
Not applicable.
Funding
Funding: The present study was supported by Scientific Research improvement program of Beijing Chest Hospital (grant no. Kj2021cx009).
Availability of data and materials
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.
Authors' contributions
FW, YH and XY wrote the manuscript. YH, SL, LZ and FW participated in design of the study. FW, XY and LZ were involved in acquisition of data. FW, SL and XY participated in analysis and interpretation of data. FW and SL confirm the authenticity of all the raw data. All authors have read and approved the final manuscript.
Ethics approval and consent to participate
The studies involving human participants were reviewed and approved (approval no B2018-011) by Ethics Committee of Sun Yat-Sen University Cancer Center (Guangzhou, P.R. China and Beijing Chest Hospital Institutional Review Board (Beijing, P.R. China). The participants provided written informed consent to participate in this study.
Patient consent for publication
Not applicable.
Competing interests
The authors declare that they have no competing interests.
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