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Response of primary tumor and lymph node in non-small cell lung cancer after neoadjuvant immunotherapy: a pooled analysis

The good pathological response of primary tumors (PTs) to neoadjuvant immunotherapy has been acknowledged in non-small cell lung cancer (NSCLC), however, it remains unclear whether neoadjuvant immunotherapy shows consistent effects in metastatic lymph nodes (LNs). We compared the pathological response of PT and nodal downstaging using a pooled analysis to assess the effect of neoadjuvant immunotherapy on LNs. Original articles reporting the tumor major pathological response (ypT(MPR)), pathological complete response (ypT0) and nodal downstaging following neoadjuvant immunotherapy in NSCLC were retrieved. The OR and 95% CI were calculated by Review Manager V.5.3. Subgroup analysis was performed according to the neoadjuvant therapy regimen used. A total of 209 patients from 6 studies were included in this analysis. The frequency of nodal downstaging was comparable to that of ypT(MPR) (OR 1.31; 95% CI 0.84 to 2.05; p=0.24). Interestingly, ypN0 was observed more frequently than ypT0 (OR 3.26; 95% CI 2.06 to 5.16; p<0.0001). However, this difference was not observed in the subgroup of cN2 patients who underwent immune checkpoint inhibitor monotherapy (OR 1.58; 95% CI 0.56 to 4.48; p=0.39). Neoadjuvant immunotherapy results in satisfactory response in metastatic LN. Patients had a high probability of node clearance when ypT0 was confirmed, especially in patients treated with immunochemotherapy.


INTRODUCTION
The CheckMate 816 trial proved that neoadjuvant immunotherapy is superior to neoadjuvant chemotherapy in locally advanced non-small cell lung cancer (NSCLC). 1 Immunotherapy has been associated with unprecedented high pathological response rates in recent trials, with major pathological response (MPR) and pathological complete response (pCR) rates ranging from 18% to 83% and 4.9% to 63%, respectively. [2][3][4][5][6][7] MPR, defined as no more than 10% viable tumor remaining within the primary tumor (PT) bed and lymph node (LN) after neoadjuvant therapy, was used as a surrogate endpoint of overall survival (OS) and diseasefree survival (DFS) in most neoadjuvant immunotherapy trials. However, except for the CheckMate 816 trial, 1 the evaluation of the exact percentage of viable tumor cells in LNs is scarcely reported, and only some trials have reported the nodal downstaging rate, that is, evidence of the efficacy of neoadjuvant immunotherapy for LNs is lacking.
Indirect comparison can offer powerful evidence if direct evidence is absent. We compared the pathological response of PT and nodal downstaging using a pooled analysis to assess the effect of neoadjuvant immunotherapy for LNs.

MATERIALS AND METHODS Data sources and search strategy
MeSH terms, including non-small cell lung cancer, neoadjuvant therapy, and immunotherapy, as well as their combinations, were used to search the PubMed, Embase, Cochrane Library electronic databases and conference abstracts for clinical trials. The detailed search strategy and inclusion criteria are presented in online supplemental materials.

Data extraction
In this study, we defined MPR in PT as ypT(MPR) and pCR in PT as ypT0. The following information was extracted: ypT(MPR), ypT0, clinical LN metastasis, clinical mediastinal LN metastasis (cN2), nodal downstaging, and nodal clearance (ypN0). Other details such as the immune checkpoint inhibitor (ICI) drug and dose and sample size are also shown in the information sheet.

Statistical analysis
Nodal downstaging, ypN0, ypT(MPR), and ypT0 were recoded into dichotomous Open access variables, which were further compared using OR. All results were reported with 95% CIs. Statistical significance was considered when p<0.05. Heterogeneity was evaluated with χ 2 and I 2 tests. The fixed effects mode was used when I 2 <50%. Subgroup analyses were performed by dividing the neoadjuvant regimens into single-agent ICI and immunochemotherapy subgroups. Possible publication bias was examined by funnel plots and Egger's test.

Risk of bias assessment
The Cochrane Handbook was used to assess the quality of randomized control trials and the quality of prospective phase I or phase II clinical trials was assessed using the Newcastle-Ottawa Scale.

Eligible studies
Six studies, 2-7 with a total of 209 enrolled patients, were included in the final analysis, (online supplemental figure 1). Details for the included studies are shown in online supplemental  1D).

ypT(MPR) versus ypN0
The ability of neoadjuvant immunotherapy to induce ypT(MPR) was similar to that of ypN0 (OR 0.81; 95% CI 0.52 to 1.25; p=0.34) and this did not differ between the two subgroups ( figure 1E). In cN2 patients, we found a tendency that ypT(MPR) was more likely to occur than nodal clearance, and the difference almost reached a  1F).

DISCUSSION
To our knowledge, this study is the first to compare the pathological response in the PT and nodal downstaging of NSCLC following neoadjuvant immunotherapy. The findings indicate that neoadjuvant immunotherapy leads to a substantial response in metastatic LNs. Nodal downstaging has been widely seen as a positive independent prognostic factor of NSCLC after neoadjuvant therapy. The long-term follow-up outcome of a multicenter phase II trial showed that mediastinal downstaging was associated with OS and DFS in cN2 NSCLC patients following neoadjuvant chemotherapy. 8 Another study discovered that only MPRypN0 rather than MPRypN1-2 could accurately predict the DFS of NSCLC after complete resection. 9 Based on the relative evidence for neoadjuvant chemotherapy, node downstaging or nodal clearance may play a critical role in long-term survival after neoadjuvant immunotherapy. Considering the better response of LNs to neoadjuvant immunotherapy, a reasonable ratiocination is that a certain number of patients might have nodal downstaging or nodal clearance despite failing to achieve an MPR status in their PTs. These patients might also benefit from neoadjuvant immunotherapy due to the downstaging of the disease. This phenomenon reminds us that a careful evaluation of the response in LNs is necessary for assessing the efficacy of neoadjuvant immunotherapy.
Although neoadjuvant immunotherapy was more effective in nodal downstaging, one may not simply conclude that ypN0 must be present in patients with PT pCR. In the trial of neoadjuvant sintilimab, only three of six patients with PT pCR had complete tumor clearance in LNs. 6 In another trial of neoadjuvant nivolumab monotherapy, one patient with PT pCR had persistent hilar LN metastasis. 5 Therefore, a complete LN dissection is warranted in any situation.
The other important note is that subgroup analysis in cases with cN2 showed that immunochemotherapy had a greater ability of nodal downstaging than ICI monotherapy ( figure 1D). Based on this finding, we suggest immunochemotherapy as the preferred neoadjuvant regimen in patients with LN metastasis, especially cN2 Open access patients. The study of Ling et al revealed a possible explanation for the unsatisfactory capability of mediastinal downstaging under ICI monotherapy. They assessed pathological responses in surgical specimens from 31 patients with squamous cell carcinoma who received neoadjuvant sintilimab monotherapy. 10 Their results indicated a lower rate of the immune-activated phenotype in N2 LNs in N1/2-positive patients. Moreover, the percentage of inflamed morphological phenotypes in N2 LNs was lower than that in N1 LNs.
There are some limitations in this pooled analysis. First, this analysis enrolled only 6 studies consisting of 209 patients, and it is impossible to investigate the different efficacies of pathological responses among different ICIs. Second, the enrolled studies had no details about the pathologic responses of histological types. We cannot know whether there is a difference in pathological response and LN downstaging between different histological types. Finally, 22.2% of the enrolled cN2 patients did not have pathologically proven N2, which would exaggerate the ability of nodal downstaging via immunotherapy.
In conclusion, neoadjuvant immunotherapy leads to a substantial response in metastatic LNs, which further supports its application in resectable NSCLC. Preoperative immunochemotherapy may be particularly suitable for patients with LN metastasis, especially in the cN2 population.
Funding This work was supported by the National Natural Science Foundation of China Youth Science Fund Project (grant number 82002407).

Competing interests None declared.
Patient consent for publication Not applicable.
Provenance and peer review Not commissioned; externally peer reviewed.
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