Prognostic impact of multiple N2 stations in patients with non small cell lung cancer

Abstract

Objective

Lung cancer is currently the leading cause of cancer-related death in men and the second most common cause in women worldwide. In the 9th edition of the TNM classification, N2 lymph node involvement has been divided into two subgroups: N2a and N2b. In this study, we aimed to examine the differences within the N2 group and to identify factors that may affect prognosis.

Methods

Between 2002 and 2023, patients who underwent preoperative mediastinal staging (EBUS/Mediastinoscopy) and were found to have N2 involvement following lung resection for non-small cell lung cancer across 7 different clinics were included in the study. A total of 149 patients met the inclusion criteria. Of these, 98 had single-station N2 involvement, while 51 had multiple-station N2 involvement. The groups were evaluated in terms of parametric and non-parametric variables using Student’s t-test and Chi-square analysis. Survival analysis was performed using the Kaplan-Meier method and Cox regression analysis. A p-value of < 0.05 was considered statistically significant.

Results

When comparing the groups based on demographic data, the mean age was 61.3 ± 8.2 years in patients with single-station N2 involvement and 59.6 ± 8.3 years in those with multiple-station N2 involvement (p = 0.979). No statistically significant difference was observed between the groups in terms of sex (p = 0.456). There was no significant difference in overall survival between the two groups (p = 0.675). However, adenocarcinoma diagnosis, TNM stage, and receipt of neoadjuvant therapy were identified as statistically significant factors associated with survival (p = 0.024, p = 0.006, and p < 0.001, respectively). In the Cox regression analysis, both pathological diagnosis and neoadjuvant therapy emerged as independent prognostic factors for survival (p = 0.046 and p < 0.001, respectively).

Discussion

Identifying prognostic factors in NSCLC patients with N2 involvement is crucial for determining appropriate treatment and follow-up strategies. In our study, patients with single and multiple N2 involvement exhibited similar demographic characteristics. When the two groups were evaluated in terms of survival, patients diagnosed with adenocarcinoma, those at Stage 3 A, and those who had not received neoadjuvant therapy were found to have significantly better survival outcomes. Our findings also indicated that patients with adenocarcinoma and unexpected N2 involvement had better survival. Independent negative prognostic factors included a non-adenocarcinoma diagnosis and prior neoadjuvant therapy. In cases of NSCLC with multiple N2 involvement, those diagnosed with non-adenocarcinoma type or who had received neoadjuvant therapy should be considered at higher risk for poor prognosis.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12672-026-05325-1.

Background

Lung cancer is one of the leading causes of cancer-related deaths. Approximately 1.8 million people die from it each year, accounting for 18% of all cancer-related mortality [1]. Non-small cell lung cancer (NSCLC) is the most common histological type, representing approximately 85% of lung cancer cases in the United States [2]. The TNM tumor staging system has been in use to guide appropriate treatment strategies and improve patient survival. In the 8th edition of this system, the “N” component refers to lymph node metastases. Specifically, N2 denotes the presence of metastases in at least one ipsilateral paratracheal or subcarinal lymph node station. Tumors with N2 disease range from Stage IIIA to IIIB, depending on their T and M classifications.

In 2024, the 9th edition of the TNM staging system was introduced. In this edition, two distinct N2 subcategories, which are predicted to differ in terms of survival outcomes, have been defined. Accordingly, N2a indicates the presence of single-station involvement in the aforementioned lymph node stations, while N2b denotes multiple-station involvement. These newly separated N2 groups have been assigned to different stages than in the previous classification. The stages now range from Stage IIB to IIIB [3]. The widely acknowledged heterogeneity of N2 disease supports the necessity of the recent subclassifications. Indeed, many previous studies have identified differences in survival between patients with single- versus multiple-station N2 involvement [4].

The selection of treatment modalities in N2 disease remains a subject of ongoing debate due to the broad spectrum it encompasses — from Stage I–IIA disease, where surgery followed by low-dose neoadjuvant therapy or radiotherapy may offer a potential cure, to Stage IV disease, where treatment invariably includes adjuvant chemotherapy. As a result, management approaches are often multimodal. In patients with Stage IIIA disease, early outcomes have been reported for local resection via VATS, robot-assisted thoracic surgery (RATS), and thoracotomy. However, current studies on this subject remain insufficient [5]. Although the choice of treatment for clinically diagnosed patients with various T stages continues to vary on a case-by-case basis, a general consensus has emerged: surgery-inclusive approaches are preferred in patients with single-station N2 involvement, while surgical resection is generally avoided in cases with multiple N2 involvement, except in selected cases [6]. While the benefit of neoadjuvant chemotherapy has been demonstrated in NSCLC patients undergoing surgical treatment, no clear comparison has been made regarding its efficacy between single- and multiple-station N2 disease [7]. As for postoperative radiotherapy, it has been shown not to improve prognosis on its own, and decisions regarding its use should be made on a case-by-case basis [8]. A meta-analysis has also revealed that there is no significant difference between patients receiving neoadjuvant chemotherapy or chemoradiotherapy prior to surgical resection and those receiving the same neoadjuvant treatments prior to radical radiotherapy [9]. Recent studies have also reported that perioperative immunotherapies combined with chemotherapeutic agents improve patient survival. However, there is no observed difference in efficacy between single and multiple N2 involvement [10, 11]

There is a limited number of studies in the current literature comparing the diagnostic and therapeutic characteristics of these two groups. In our study, we aimed to identify the clinical and survival differences between these two highly heterogeneous groups and to determine prognostic factors.

Methods

Our study was conducted as a retrospective analysis covering 7 different centers where lung cancer was treated and followed between 2002 and 2023. This study was approved by the Istanbul University-Cerrahpaşa Ethics Committee (Approval Code: 2025/53, Date: 13.02.2025). A total of 149 patients diagnosed with N2 disease through invasive mediastinal staging and lung resection were included. 98 of them had single-station N2 involvement, while 51 of them had multiple-station N2 involvement.

The patients’ demographic data (age, sex), history of comorbidities, presence of additional malignancies, receipt of chemotherapy and/or radiotherapy, histopathological type, location and size of the tumor, LDH levels, findings from EBUS-TBNA, mediastinoscopy, and PET/CT scans were retrospectively reviewed. Particular attention was given to N-stage involvement, specifically whether single or multiple mediastinal stations were affected. The study included patients over the age of 18 who underwent surgical treatment for lung cancer. Patients who were not eligible for surgery or did not meet the age criteria were excluded. Tumor staging was performed according to the 8th edition of the TNM Classification of Malignant Tumors for lung and pleural cancers.

Preoperative mediastinal involvement was assessed in 226 patients who were initially considered for inclusion in the study, using EBUS, mediastinoscopy, or video-assisted mediastinoscopic lymphadenectomy (VAMLA), along with lung resection findings. To maintain a targeted cohort, patients with N1 lung cancer and those without mediastinal involvement (N0) were excluded from the study, resulting in a final sample of 149 patients. Of these, 98 patients (65.8%) had single-station N2 disease, and 51 patients (34.2%) had multiple-station N2 disease. These two groups were compared in terms of both parametric and categorical variables (Fig. 1, Flowchart).

Fig. 1.

Flowchart showing the inclusion and exclusion criteria for the study

For the comparison of patients with single-station and multiple-station N2 involvement, the Student’s t-test was used for parametric variables, while the Chi-square test was applied for categorical variables. Survival analyses were performed using the Kaplan-Meier method and Cox regression analysis. Survival analyses were initially performed using univariable methods. Variables with p < 0.20 in the univariable analysis, together with clinically meaningful variables known to have prognostic significance based on the literature, were included in the multivariable Cox regression model. The multivariable model incorporated histological subtype (adenocarcinoma vs. non-adenocarcinoma), TNM stage, pattern of N2 involvement (single-station vs. multiple-station), and history of neoadjuvant therapy. The Cox regression analysis was performed considering the proportional hazards assumption, and the results were reported as hazard ratios (HR) with 95% confidence intervals (CI). All statistical analyses were conducted using SPSS version 30.00 (IBM Corp.; Armonk, NY, USA). A p-value of < 0.05 was considered statistically significant.

Results

When the groups were evaluated in terms of demographic data, the mean age of the patients with single N2 involvement was 61.3 ± 8.2 years, while it was 59.6 ± 8.3 years in patients with multiple N2 involvement. There was no statistically significant difference in age between the groups (p = 0.979). Regarding sex distribution, male sex was predominant in both groups, with 83.67% in the single N2 group and 88.24% in the multiple N2 group. There was no statistically significant difference in sex distribution between the groups (p = 0.456) (Tables 1, 2).

Table 1.

Comparison of groups in terms of parametric data

	Single N2 (98 Patients)	Multiple N2 (51 Patients)	p Value	95% CI
Age	61.3 ± 8.2	59.6 ± 8.3	0.979	-1.0-4.6
Smoking	35 ± 24	39 ± 31	0.454	-12.8-5.1
LDH	242 ± 118	255 ± 166	0.271	-61.6-33.5
Size of tumor	4.3 ± 2.4	4.1 ± 2.0	0.085	-0.5-1.0

Table 2.

Comparison of groups in terms of categoric data

	Single N2 (98 Patients)	Multiple N2 (51 Patients)	p Value	ODDS Ratio 95% CI
Sex
Female	16 (16.3%)	6 (11.8%)	0.456	0.68 (0.03–1.87)
Male	82 (83.7%)	45 (88.2%)
T stage
1a	5 (5.9%)	2 (4.3%)	0.788	0.73 (0.32–1.67)
1b	11 (12.9%)	3 (6.4%)
1c	15 (17.7%)	8 (17.0%)
2a	20 (23.5%)	14 (29.8%)
2b	16 (18.8%)	8 (17.0%)
3a	18 (21.2%)	12 (25.5%)
Surgical procedure
Lobectomy	81 (82.7%)	40 (78.4%)	0.806	0.51 (0.07–3.73)
Bilobectomy	5 (5.1%)	2 (3.9%)
Pneumonectomy	10 (10.2%)	7 (13.7%)
Wedge resection	2 (2.0%)	2 (3.9%)
Location
RUL	30 (30.6%)	21 (41.2%)	0.462	0.63 (0.31–1.27)
RML	4 (4.1%)	0 (%0)
RLL	15 (15.3%)	8 (15.6%)
LUL	27 (27.5%)	13 (25.5%)
LLL	22 (22.5%)	9 (17.7%)
Side
Right	49 (50%)	29 (56.9%)	0.426	0.76 (0.38–1.5)
Left	49 (50%)	22 (43.1%)
Mediastinoscopy (+)	65 (66.3%)	26 (51.0%)	0.068	0.53 (0.27–1.05)
EBUS (+)	34 (34.7%)	21 (41.2%)	0.437	1.32 (0.66–2.64)
Diagnosis
Adenocarcinoma	50 (50.0%)	27 (53.0%)	0.178	0.56 (0.28–1.12)
Squamous cell carcinoma	37 (37.7%)	13 (25.5%)
Adenosquamous carcinoma	8 (8.2%)	10 (19.5%)
Other	3 (3.1%)	1 (2.0%)
Neoadjuvant Therapy (+)	51 (52.0%)	29 (56.9%)	0.575	1.22 (0.62–2.40)
Additional Malignancy (+)	4 (4.1%)	2 (3.9%)	0.962	0.96 (0.17–5.42)
Comorbidity	58 (59.2%)	27 (53.0%)	0.465	0.78 (0.39–1.53)

There were no statistically significant differences between the groups in terms of tumor size, T stage, or pathological diagnosis (p = 0.085, 0.788, and 0.178, respectively). Likewise, clinical variables such as serum LDH level, type of surgical resection performed, history of neoadjuvant therapy, and postoperative hospital stay duration did not differ significantly between the groups (p = 0.271, 0.806, and 0.575, respectively) (Table 1).

In the group with single-station N2 disease, the long-term survival rate was 34.7%, and the median survival time was 85.9 ± 11.0 months (95% CI: 64.42-107.64 months). In the group with multiple N2 disease, the long-term survival rate was 39.2%, and the median survival time was 105.9 ± 17.8 months (95% CI: 71.12-140.84 months). There was no statistically significant difference in survival between the two groups (p = 0.675) (Fig. 2).

Fig. 2.

Single and multiple N2 survival curve - Kaplan Meier analysis

The long-term survival rate was 45.5% in patients with a pathological diagnosis of adenocarcinoma, whereas it was 26.4% in those with non-adenocarcinoma tumors. The median survival time was 105.9 ± 13.7 months (95% CI: 79.12–132.91 months) in the adenocarcinoma group, and 75.8 ± 13.2 months (95% CI: 49.93–101.72 months) in the non-adenocarcinoma group. Survival was found to be significantly better in patients with adenocarcinoma (p = 0.024) (Fig. 3).

Fig. 3.

Diagnosis survival curve- Kaplan Meier analysis

According to the TNM staging system, patients with stage 3 A disease had a long-term survival rate of 42.6% and a median survival time of 114.9 ± 13.1 months (95% CI: 89.34-140.41 months), while in stage 3B patients, the corresponding values were 22.9% and 61.7 ± 13.5 months (95% CI: 35.42–88.13 months). This difference was found to be statistically significant (p = 0.006) (Fig. 4).

Fig. 4.

TNM stage survival curve - Kaplan Meier analysis

In patients who did not receive neoadjuvant therapy, the long-term survival rate was 50.7%, and the median survival time was 135.1 ± 16.1 months (95% CI: 103.72-166.61 months). In contrast, among those who did receive neoadjuvant therapy, the long-term survival rate was 23.8%, and the median survival time was 50.8 ± 8.1 months (95% CI: 34.92–66.73 months). A statistically significant difference was observed between the two groups (p < 0.001) (Fig. 5).

Fig. 5.

Neoadjuvant therapy survival curve - Kaplan Meier analysis

In patients with adenocarcinoma and single N2 involvement who did not receive neoadjuvant therapy, the long-term survival rate was 56%. However, the long-term survival rate in patients with non-adenocarcinoma tumors and multiple N2 involvement who received neoadjuvant therapy was 30.6%. The T stage did not have a significant impact on survival (p = 0.073) (Tables 3, 4) (Fig. 6).

Table 3.

Comparison of survival data between groups using Kaplan-Meier analysis

	Long term survival rates (%)	Median survival time (Months)	95% confidence interval
Neoadjuvant Therapy (-), Diagnosed with adenocarcinoma,Single N2 Patients	56.0%	137.8 ± 22.6	93.52-182.13
Neoadjuvant Therapy (+), Diagnosed with Non-adenocarcinoma, Multiple N2 Patients	30.6%	84.4 ± 10.9	63.02-105.94

Table 4.

Cox regression analysis results

	p Value	95% confidence interval	Hazard ratio
Diagnosis	0.046	0.43–0.99	0.66
TNM Stage	0.975	0.54–1.89	1.01
T Stage	0.085	0.98–1.41	1.18
Neoadjuvant Therapy	< 0.001	0.30–0.71	0.45

Fig. 6.

All variables survival curve - Kaplan Meier analysis

In multivariate Cox regression analysis, adenocarcinoma histology (HR: 0.66, 95% CI: 0.43–0.99, p = 0.046) and absence of neoadjuvant therapy (HR: 0.45, 95% CI: 0.30–0.71, p < 0.001) were independently associated with improved survival.

Discussion

In our study, single N2 involvement, a diagnosis of adenocarcinoma, and not receiving neoadjuvant therapy were identified as positive prognostic factors.

Patients diagnosed with adenocarcinoma generally have a significantly better prognosis, as past studies have shown that adenocarcinomas, which are less strongly associated with smoking and more commonly found in women than men, are associated with significantly better survival [12]. The same tendency continues in cases of non-small cell lung cancer (NSCLC) with N2 involvement. While our findings agree with the literature in this regard, they contradict the known outcomes regarding neoadjuvant therapy [13]. According to our study, patients who received neoadjuvant therapy had worse survival compared to those who did not; however, this may be due to neoadjuvant therapy being applied more frequently to patients with multiple N2 disease, who are more likely to have a worse prognosis.

The absence of a significant survival difference between single-station and multiple-station N2 disease in our cohort may initially appear unexpected. However, all patients in this study underwent preoperative invasive mediastinal staging (EBUS, mediastinoscopy, or VAMLA), which likely excluded patients with clinically evident and extensive mediastinal involvement from surgical treatment. Therefore, our study represents a surgically treated and carefully selected cohort. It is possible that the more aggressive subset of multiple-station N2 patients was not included, leading to a degree of selection bias. In addition, a proportion of postoperative N2 cases may correspond to the so-called “unexpected (surprise) N2” group described in the literature, which has been associated with more limited tumor burden and potentially more favorable tumor biology. Thus, the similar survival outcomes between the groups may reflect the heterogeneous nature of N2 disease and the impact of meticulous preoperative staging on patient selection.

Induction chemoradiotherapy has been reported in the literature for patients with surgically resectable stage IIIA (N2) non-small cell lung cancer [14, 15]. Induction therapy, compared with surgery alone, has been shown to improve overall survival and disease-free survival [14, 15]. Due to the recent success of neoadjuvant immunotherapy, neoadjuvant treatment modalities should be considered before surgery in patients with multiple N2 lesions [16–18]. Expanding the data from our study may further demonstrate the effectiveness of neoadjuvant immunotherapy. With adequate preoperative mediastinal staging, neoadjuvant immunotherapy options should be considered for patients with N2 disease [16–18]. In addition, adjuvant chemoimmunotherapy after surgery has been shown to improve overall survival and recurrence-free survival [19]. However, in our study, the poorer survival observed in patients receiving neoadjuvant therapy may reflect patient selection and tumor biology rather than a direct adverse effect of the treatment itself. Patients with more advanced disease stages, higher tumor burden, or more aggressive clinical characteristics may have been more likely to receive neoadjuvant therapy. This situation is described in the literature as ‘confounding by indication,’ in which the treatment group inherently carries worse baseline prognostic features, thereby influencing survival outcomes. Moreover, as our study included only patients with pathologically confirmed N2 disease, those with persistent residual N2 involvement despite neoadjuvant therapy may represent a biologically more resistant subgroup with limited treatment response. Therefore, the identification of neoadjuvant therapy as an independent negative prognostic factor in the multivariable analysis should be interpreted within the context of tumor biology and treatment response.

Additionally, in accordance with the TNM staging system, the survival of patients with stage 3 A disease is better than that of patients with stage 3B disease. This indicates that our data are consistent with the literature and that the staging was regulated correctly.

In our study, the groups had similar findings in terms of demographic characteristics, tumor size, laboratory values, and surgical features. This suggests that the study, which was designed as a multicenter retrospective analysis, adhered to appropriate staging criteria and that preoperative mediastinal staging was performed carefully. The better survival observed in cases with a diagnosis of adenocarcinoma and unexpected N2 involvement could also be associated with thorough clinical evaluation during the preoperative period.

Although this study presents results consistent with the literature, it has certain limitations. The retrospective nature of the study and the potential data loss due to the heterogeneity of the groups may introduce potential biases. The relatively limited sample size, particularly in the multiple-station N2 subgroup, may reduce statistical power and should be considered when interpreting the results. Furthermore, the differences in the clinics where the data were collected may lead to variations in treatment approaches, and the wide time span further supports these discrepancies. The inclusion period of our study (2002–2023) may introduce potential time-related confounding due to the increasing adoption of minimally invasive surgical techniques and advances in systemic treatment strategies over time. To evaluate this possibility, a separate survival analysis was conducted for patients operated between 2015 and 2023. No significant survival difference was observed between single- and multiple-station N2 groups within this subgroup. Additionally, none of the patients included in our cohort received neoadjuvant immunotherapy. These findings suggest that the observed results are unlikely to be primarily driven by a period effect. Nevertheless, the extended study period remains a limitation of the study. In the future, prospective studies with larger patient cohorts could provide a stronger validation of the findings.

Conclusions

Our findings highlight the prognostic relevance of histopathological subtype in stage III non-small cell lung cancer. Adenocarcinoma histology was associated with improved survival outcomes in patients with pathological N2 disease. Although no significant survival difference was observed between single- and multiple-station N2 involvement in the overall analysis, this finding may reflect careful preoperative staging and patient selection in this surgically treated cohort. The association between receipt of neoadjuvant therapy and poorer survival should be interpreted with caution, as this likely reflects underlying tumor burden, disease biology, and potential confounding by indication rather than a direct detrimental effect of the treatment itself. Prospective, well-controlled multicenter studies are warranted to further clarify the prognostic impact of N2 subcategories and optimize treatment strategies for N2-positive NSCLC.

Author contributions

Conceptualization: GÖI, AT; Methodology: GÖI, AT, ZSA, GB; Software: GÖI, AT, ZSA, GB; Validation: GÖI, AT, ZSA, GB; Formal analysis: GÖI, AT, ZSA, GB; Investigation: GÖI, AT, ZSA, GB; Resources: GÖI, AT, ZSA, GB, SY, NF, PAK, DK, GA, MM, SŞEG, BK, ÜY; Data curation: GÖI, AT, ZSA, GB, SY, NF, PAK, DK, GA, MM, SŞEG, BK, ÜY; Writing – original draft: GÖI, AT, ZSA, GB, SY, NF, PAK, DK, GA, MM, SŞEG, BK, ÜY; Writing – review & editing: GÖI, AT, ZSA, GB, SY, NF, PAK, DK, GA, MM, SŞEG, BK, ÜY; Visualization: GÖI, AT, ZSA, GB, SY, NF, PAK, DK, GA, MM, SŞEG, BK, ÜY; Supervision: GÖI, AT, ZSA, GB, SY, NF, PAK, DK, GA, MM, SŞEG, BK, ÜY. All authors read and approved the final manuscript.

Funding

No funding was received for this study.

Data availability

The datasets generated and analyzed during the current study are available from the corresponding author upon reasonable request.

Declarations

Ethics approval and consent to participate

This study was approved by the Istanbul University-Cerrahpaşa Ethics Committee (Approval No: 2025/53, Date: 13.02.2025). Written informed consent was obtained from all patients, and the study was conducted in accordance with the principles of the Declaration of Helsinki.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.