Pathological responses of primary tumor and lymph nodes in non-small cell lung cancer after neoadjuvant chemoimmunotherapy: a retrospective real-world study

Introduction

Non-small cell lung cancer (NSCLC) is the leading cause of cancer death in China and the world (1). Neoadjuvant chemotherapy (NCT) alone has been shown to have limited capability to improve the survival rate (2). For locally advanced NSCLC, the emergence of immune checkpoint inhibitors (ICIs) has thoroughly changed the neoadjuvant therapy regimen and the CheckMate 816 trial has demonstrated that neoadjuvant chemoimmunotherapy (NCIT) provides more survival benefits than NCT (3,4). Major pathologic response (MPR) is a common alternative endpoint in many ongoing or completed clinical trials evaluating neoadjuvant immunotherapy (NIT) for NSCLC (5). However, current clinical studies on NCIT have shown very different results for MPR, ranging from 36.9% in the CheckMate 816 study to 82.9% in the NADIM study (4,6).

In recent years, the association between primary tumor and lymph nodes (LNs) responses to neoadjuvant therapy and survival benefits has been investigated. It has been reported that the combined responses of primary tumor and LNs after NCT in patients with NSCLC showed favorable prognostic significance (7,8). The consistently good response observed in the primary tumor and LNs was associated with a good survival benefit. However, some studies have reported that 21.05–53.2% of patients still have differences in response between the primary tumor and LNs (4,6). There have been case reports of inconsistent response of LNs in patients who have achieved pathological complete response (pCR) of the primary tumor. There is limited evidence comparing different responses of primary tumor and LNs in patients with resectable NSCLC. Hence, this retrospective real-world analysis intended to evaluate the clinical and pathological responses of primary tumor and LNs, and long-term outcomes in NSCLC patients after NCIT. We present this article in accordance with the STROBE reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-1011/rc).

Methods

Patient population

We included resectable NSCLC patients who had received neoadjuvant therapy and had available clinicopathological data from March 2021 to June 2023 at the Department of Thoracic Surgery, Shandong Cancer Hospital and Institute. The flow chart of study design is shown in Figure 1. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013) and approved by the Ethics Committee of the Shandong Cancer Hospital and Institute (No. SDTHEC2024002005). The requirement for individual consent for this retrospective analysis was waived. The inclusion criteria were as follows: (I) age 18 years or older; (II) no previous treatment for lung cancer; (III) Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0 or 1; (IV) underwent NCIT and surgery; and (V) histologically confirmed NSCLC. The exclusion criteria were as follows: (I) history of malignancies in the past 5 years; (II) previous local radiotherapy or any systemic antitumor therapy; (III) unstable systemic disease; (IV) history or current diagnosis of interstitial lung disease (ILD); and (V) exploratory thoracotomy.

Figure 1 Flow chart of study design. NSCLC, non-small cell lung cancer.

This study was based on the 8^th edition of the Union for International Cancer Control/American Joint Committee on Cancer (UICC/AJCC) primary tumor, regional LNs involvement, and distant metastases (TNM) staging system. All patients received multi-disciplinary treatments (MDTs) to assess their condition and determine an appropriate protocol before starting treatment. The main preoperative regimens consisted of platinum-based dual-drug chemotherapy and programmed cell death-ligand 1 (PD-L1)/programmed cell death protein 1 (PD-1) inhibitors every 3 weeks.

The clinical responses of the primary tumor and LNs were evaluated after every two NCIT cycles according to the Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 (9). The evaluation of the target lesions was divided into complete response (CR), partial response (PR), stable disease (SD), progressive disease (PD), and overall response (OR).

All patients underwent radical surgical resection of lung cancer 4–6 weeks after the last NCIT. The pulmonary lesion was excised via lobectomy, sublobectomy, sleeve lobectomy, or pneumonectomy. Surgical specimens were histopathologically examined, and the activity of the tumor and LNs was evaluated by two pathologists. T and N downstaging were defined as T or N category declines. MPR was defined as residual viable tumor cells less than 10%, and pCR was defined as no residual viable tumor (including primary tumor and LNs) (10). Yield pathological tumor MPR (ypTMPR) was defined as residual viable primary tumor cells less than 10%, and yield pathological tumor pCR (ypTpCR) was defined as no residual viable primary tumor. All selected patients received a regular outpatient review and telephone follow-up. The follow-up ended on 1 March 2023. Overall survival (OS) was defined as the time from the initial diagnosis to death from any cause and progression-free survival (PFS) was defined as the time from the initial diagnosis to progression of disease, recurrence of disease, or death from any cause.

Statistical analysis

Categoric variables were expressed as numbers or percentages and evaluated with Chi-squared or Fisher’s exact test. Continuous data were presented as mean [interquartile range (IQR)] or mean ± standard deviation and were compared using the two-sample Student’s t-test. The Kaplan-Meier method was used to estimate median PFS and OS and two-sided 95% confidence intervals (CIs) for time to event. We estimated hazard ratios (HRs) and 95% CIs using a Cox proportional hazards regression model. All P values were reported by two-sided analyses, and the statistical significance level was set at less than 0.05. Subgroup analysis adjusted by T stage and N stage was adopted to investigate the impact of adjuvant treatment on survival outcomes. Statistical analysis was performed with SPSS 25.0 software (IBM Corp., Armonk, NY, USA).

Results

Patients

We excluded two patients who underwent NCIT because they had only undergone exploratory thoracotomy. In total, 204 patients met the inclusion criteria (Figure 1). Table 1 summarizes the clinical and pathological characteristics of patients. The patients were predominantly male (85.8%) and ever-smokers (66.2%), with a median age of 63 (IQR, 56–67.75) years and a median body mass index (BMI) of 23.94 (IQR, 21.80–25.97) kg/m². The main pathology was primary squamous cell carcinoma (SCC) (141, 69.1%). More than half of the patients (137, 67.2%) received 2 cycles of NCIT. Most patients received lobectomy (149, 73.0%), with a smaller proportion undergoing bilobectomy (26, 12.7%), sleeve lobectomy (21, 10.3%), or pneumonectomy (6, 2.9%). No significant difference was observed in intraoperative bleeding (P=0.51 and P=0.54) and operation time (P=0.57 and P=0.58) between the MPR and pCR groups, respectively.

Clinical and pathological response

Most patients were classified as clinical T2 (cT2) (97, 47.5%) and clinical N2 (cN2) (103, 50.5%). After NCIT, 96 (47.1%) achieved PR and 19 (9.3%) had a CR, resulting in an OR rate (ORR) of 56.4%. As shown in Table 1, 77 (37.7%) patients achieved pCR and 127 (62.3%) patients achieved MPR. Patients who were male (pCR, P=0.01; MPR, P=0.004), had SCC (pCR, P=0.02; MPR, P=0.001), and ORR (pCR, P<0.001; MPR, P<0.001) demonstrated significantly higher rates of pCR and MPR (Table 2). There was no significant correlation between pathological response and clinical stage of tumor (cT) (pCR, P=0.75; MPR, P>0.99), clinical stage of LNs (cN) (pCR, P=0.54; MPR, P=0.09), or clinical stage of TNM (cTNM) (pCR, P=0.79; MPR, P=0.20). However, there was a significant difference between pathological response and yield clinical stage of primary tumor (ycT) (pCR, P<0.001; MPR, P=0.004). In terms of re-staging after treatment, stage ycIII accounted for the highest proportion (53.9%), but postoperative pathology confirmed that stage ypIII only accounted for (19.1%), re-staging to ypI accounted for the greatest proportion (37.7%). A total of 188 patients (92.2%) had T downstaging and 118 patients (57.8%) had N downstaging. Only 1 patient (0.5%) had T upstaging, but 41 patients (20.1%) had N upstaging. Pathological N upstaging was observed in only 9 (4.4%) patients. The detailed stages [cTNM, yield clinical stage of TNM (ycTNM), yield pathological stage of TNM (ypTNM)] are shown in Figure 2A-2C.

Figure 2 Changes in stages. (A) cTNM; (B) ycTNM; (C) ypTNM. cTNM, clinical stage of primary tumor, regional lymph nodes involvement, and distant metastases; ycTNM, yield clinical stage of primary tumor, regional lymph nodes involvement, and distant metastases; ypTNM, yield pathological stage of primary tumor, regional lymph nodes involvement, and distant metastases.

Survival outcomes

The median follow-up time for all patients in this study was 23 months. The survival analyses for OS (Figure 3A,3B) and PFS (Figure 4A,4B) compared MPR and pCR. Patients with MPR (P=0.004) and pCR (P=0.02) experienced prolonged PFS, but no extension of OS (MPR, P=0.08; pCR, P=0.15). Survival analysis also showed that compared to the yield pathological LNs stage (ypN)(1+2) group, the ypN(0) group had a longer PFS (Figure 5A,5B) (P=0.043). Rates of progression among patients with MPR and non-MPR were 9.4% (12/127) and 24.7% (19/77) (P=0.003), and those among patients with pCR and non-pCR were 7.8% (6/77) and 19.7% (25/127) (P=0.12). A total of 31 (15.2%) patients experienced local recurrence or distant metastasis, and 24 (11.8%) patients died. The death rate among patients with MPR and non-MPR was 8.7% (11/127) and 16.9% (13/77) (P=0.08), respectively, and that among patients with pCR and non-pCR was 7.8% (6/77) and 14.2% (18/127) (P=0.17), respectively.

Figure 3 OS among patients with MPR (A) and pCR (B). MPR, major pathologic response; pCR, pathological complete response; OS, overall survival.

Figure 4 PFS among patients with MPR (A) and pCR (B). MPR, major pathologic response; pCR, pathological complete response; PFS, progression-free survival.

Figure 5 PFS among patients with ypN (A,B). ypN, yield pathological of regional lymph nodes; PFS, progression-free survival.

ypT versus ypN

The overall ypTMPR rate was 62.3%, ypTpCR rate was 40.7%, and the ypN0 rate was 73%. LNs downstaging to ypN0 was observed in 107 of 204 (52.5%) patients, with two cases downstaging from N3 to N0, 73 cases from N2 to N0, and 33 cases from N1 to N0 (Table 1). Notably, we found a significant association between ypTMPR/pCR and ypN. After obtaining ypTMPR, 86.6% (110/127) of patients achieved ypN0, whereas only 50.6% (39/77) of patients in the non-ypTMPR group achieved ypN0 (P<0.001). After obtaining ypTpCR, 92.8% (77/83) of patients achieved ypN0, whereas only 59.5% (72/121) of patients in the non-ypTpCR group achieved ypN0 (P<0.001).

In terms of ypTMPR and ypN (Figure 6A), Kaplan-Meier analyses demonstrated the better PFS for the ypTMPR(+)/ypN(0) group, followed by ypTMPR(−)/ypN(0), ypTMPR(+)/ypN(0), and ypTMPR(−)/ypN(1+2). The average PFS time for these groups was 35.7, 31.7, 29.4, and 28.7 months, respectively. After achieving MPR, the probability of local recurrence or distant metastasis was 7.3%, 25%, 23.5%, and 23.7%, respectively. The results showed that the PFS of the ypTMPR(+)/ypN(0) group was significantly better than that of the other groups (P=0.01). In terms of ypTpCR and ypN (Figure 6B), survival analysis showed better PFS for the ypTpCR(+)/ypN(0) group, followed by ypTpCR(−)/ypN(0), ypTpCR(+)/ypN(0), and ypTpCR(−)/ypN(1+2).

Figure 6 PFS among patients with ypTMPR/ypN (A) and ypTpCR/ypN (B). ypTMPR, yield pathological tumor major pathologic response; ypN, yield pathological of regional lymph nodes; ypTpCR, yield pathological tumor pathological complete response; PFS, progression-free survival.

To specifically assess the responses of primary tumor and LNs, survival analyses were performed to understand outcomes between groups. Using ypTMPR and ypN status (Figure 6A), four groups were reviewed in assessing PFS: ypTMPR(+)/ypN(0), ypTMPR(+)/ypN(1+2), ypTMPR(−)/ypN(0), and ypTMPR(−)/ypN(1+2). Similarly, using ypTpCR and ypN status, four groups were reviewed in assessing PFS: ypTpCR(+)/ypN(0), ypTpCR(+)/ypN(1+2), ypTpCR(−)/ypN(0), and ypTpCR(−)/ypN(1+2).

The average PFS time was 35.6, 34.5, 31, and 28.5 months, respectively (P=0.09). After achieving pCR, the probability of local recurrence or distant metastasis was 7.8%, 16.7%, 16.7%, and 24.5%, respectively.

Discussion

Many clinical trials (NADIM, CheckMate 816, and Keynote-671) have demonstrated superior PFS, OS, MPR, and pCR rates of NSCLC after NICT (4,6,11). We demonstrated a higher rate of patients with a pCR (37.7%) than the CheckMate 816 trial (24%), which was similar to that in the NADIM II trial (37%). In clinical trials, more reliable LNs sampling and pathological assessments were carried out at baseline, whereas in routine clinical practice, simplified radiological evaluation was more common for N stage patients, resulting in more early-stage patients undergoing NCIT. In addition, clinical trials have typically excluded stage I patients, and among the patients who received NCIT in our cohort, 2.5% of patients were diagnosed as stage I at the time of diagnosis. The above reasons led to a higher pCR rate in our study. The ability of NCIT to induce MPR (P=0.001) and pCR (P=0.02) in SCC was significantly higher than that in other pathological types. This also confirmed the clinical preference for NCIT in patients with SCC (9).

Although pCR was a more accurate predictive indicator, its application in NCIT was often limited by its infrequent occurrences. Currently, MPR has become an acceptable surrogate of predicting the effect of NCT and has been used as a prognostic index in some clinical trials of NIT (12,13). The MPR rate was 62.3%, and the result was similar to the pooled analysis of Zhai et al. (14). PFS in patients who achieved pCR and MPR was better than it was those who achieved non-pCR (P=0.02) and non-MPR (P=0.004). For OS, no significant difference was observed between the MPR (P=0.08) and pCR (P=0.15). It seemed that for patients who have obtained MPR or pCR, PFS was a better endpoint indicator than OS. Therefore, we adopted PFS as the end point indicator in the subgroup analysis.

Previous studies have shown that the pathological benefit (MPR or pCR) was better in patients with stage III than in patients with stage I or II (15,16). However, in our results, pathological type was the significant factor affecting pathological benefits and had little to do with clinical TNM staging.

We further compared the pathological responses of primary tumors and LNs in NSCLC patients who received NCIT. We demonstrated a significant association between ypTMPR/pCR and ypN0. We found that about 50% of patients achieved ypN0, but the primary tumor did not reach MPR or pCR. This might be because we included more patients with baseline cN0 (24.5%). Ye et al. believed that in situ immune patterns of T cells and cytotoxic T cells were different between primary tumor and metastasis LNs in NSCLC. The heterogeneity of the in situ immune patterns might result in different immune-mediated responses to NIT (17). Hence, after NCIT, it was not reliable to establish an absolute correlation between ypTMPR/pCR and ypN0. Similarly, Forde et al. and Gao et al. concluded that ypN0 could not simply be present in patients with ypTpCR (16,18).

Betticher et al. and van Meerbeeck et al. have demonstrated a positive association between LNs downstaging and improvement in OS in patients with pathologically confirmed stage IIIA NSCLC after NCT (19,20). The association between LNs responses to NCIT and OS has also been investigated (6). LNs downstaging was widely recognized as an independent prognostic factor, reflecting both radical resection of NSCLC and the effectiveness of NCIT (21). The impact of ypN status on PFS was statistically significant in this study. The ypN0 was significantly correlated with better PFS, followed by ypN1 and ypN2. Our research showed a promising result about LNs response, with a high LNs downstaging rate (57.9%) and ypN0 status (73%). As expected, LNs, a recognized organ that promotes anti-tumor immunity, was more responsive to immunotherapy.

In order to further evaluate the combined response of an NCIT regimen to primary tumor and LNs response, we conducted subgroup analysis. In this real-world study, we demonstrated that the ypTMPR(+)/ypN(0) group had a better prognosis, followed by ypTMPR(−)/ypN(0), ypTMPR(+)/ypN(0), and ypTMPR(−)/ypN(1+2). The results indicated that compared to primary tumor regression, LNs downstaging was more likely to predict PFS. It was found that the combination of ypTMPR(+) and ypN0 was associated with good PFS and should be regarded as a reliable indicator to predict the prognosis of NSCLC patients after NCIT. Corsini et al. found that MPRypN0 represented the most favorable end point after NCT (22). They emphasized that MPRypN0 was the most effective end point and should be considered as an alternative end point in future neoadjuvant trials. We validated their outcomes in the environment of NCIT, which provided more evidence for ypTMPR(+)/ypN(0) as the end point.

Moreover, our study found a significant difference between ycTNM and ypTNM. A recent report has shown that there was inconsistency between radiological and pathological assessments of tumor response in the real-world settings (23). We believed that RECIST version 1.1, which was currently available, was not timely enough to distinguish between radiological and true pathological responses. Further research was needed to establish new radiological standards that did not rely solely on CT to better reflect the efficacy of NCIT.

Another important note was that the rate of cN2 descending to pN0 was the highest, indicating that NCIT had a greater ability to descend mediastinal LNs. Ling et al. demonstrated that the percentage of inflammatory morphology and phenotype in the N1 LN was higher than that in the N2 LN in the enrolled patients (8).

Limitations

In the course of our above research, there were some small findings, but this study has several limitations. Firstly, as a single institution experience from a large, regional cancer hospital, our report might lack generalizability to other populations. Secondly, the postoperative follow-up is short. In the future, we hope to observe the 5-year PFS and OS after NCIT in a larger patient cohort. Thirdly, the efficacy of different chemotherapeutic and immunological drugs vary slightly, which might have an impact on the outcome. Finally, it is the use of a scheme used outside standard clinical practice as set out in clinical guidelines. We need more data to confirm these results.

Conclusions

Patients who achieved pCR and MPR had a better PFS than those with non-pCR and non-MPR, but OS did not. In the real-world study, we demonstrated that ypTMPR(+)/ypN(0) group had a better prognosis, followed by ypTMPR(−)/ypN(0), ypTMPR(+)/ypN(0), and ypTMPR(−)/ypN(1+2). The results demonstrated that, among patients with ypTMPR(+), those with ypN0 status could acquire better benefits from NCIT. We advocate for ypTMPR(+)/ypN(0) status as a better surrogate of PFS in resectable NSCLC patients after NCIT.

Acknowledgments

We gratefully acknowledge the role of all our colleagues, nurses, and others involved in the care of these patients.

Funding: This study was supported by the Taishan Scholar Project Special Fund (No. tsqn202312367).

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-1011/rc

Data Sharing Statement: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-1011/dss

Peer Review File: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-1011/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-1011/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by the Ethics Committee of the Shandong Cancer Hospital and Institute (No. SDTHEC2024002005). The requirement for individual consent for this retrospective analysis was waived.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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