Front-Line ICI-Based Combination Therapy Post-TKI Resistance May Improve Survival in NSCLC Patients With EGFR Mutation

Background Data on the use of immune checkpoint inhibitors (ICIs) in advanced non-small cell lung cancer (NSCLC) patients with epidermal growth factor receptor (EGFR) mutation are limited. The current study aimed to assess the efficacy of ICIs in EGFR-mutant advanced NSCLC and explore the relevant influential factors. Materials and Methods Relevant clinical data of EGFR-mutant NSCLC patients who had received ICIs were collected from multiple hospitals. The primary endpoint was progression-free survival (PFS), and the secondary endpoints were overall survival (OS), objective response rate (ORR), and relevant influential factors. Results A total of 122 advanced EGFR-mutant NSCLC patients were included in the final analysis. The total cohort had an objective response rate (ORR) of 32.0%, a median progression-free survival (mPFS) of 5.0 months, and a median overall survival (mOS) of 14.4 months. Among 96 patients with common EGFR mutations (19Del, 52 patients; L858R, 44 patients), those who were administered front-line ICI exhibited better survival benefits than those who received later-line ICI after disease progression on tyrosine kinase inhibitors (TKIs) treatment (mPFS: 7.2 months vs. 3.4 months, respectively, P < 0.0001; mOS: 15.1 months vs. 8.4 months, respectively, P <0.0001). Moreover, the efficacy of ICI-based combination therapy was better than that of ICI monotherapy (mPFS: 5.0 months vs. 2.2 months, respectively, P = 0.002; mOS: 14.4 months vs. 7.0 months, respectively, P = 0.001). Multivariate analysis showed that ICI-based combination therapy and front-line ICI administration after progression on EGFR-TKI were associated with significant improvements in both PFS and OS (P < 0.05). A high PD-L1 expression (tumor proportion score, TPS≥50%) and the EGFR L858R mutation were only significantly associated with a better PFS (P <0.05). A better Eastern Cooperative Oncology Group (ECOG) status was independently associated with a favorable OS (P <0.05). Conclusions Taken together, combination immunotherapy in front-line was associated with improvement of survival in EGFR-mutant NSCLC patients post-TKI resistance. Further prospective studies with large sample sizes are required to identify the optimal combinatorial treatment strategy.


INTRODUCTION
Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) as a standard first-line treatment for advanced non-small-cell lung cancer harboring EGFR mutation yield great efficacy but acquired resistance and disease progression are inevitable (1)(2)(3). Salvage treatment options following available TKI failure are limited; chemotherapy serves as the primary modality with unsatisfactory efficacy (4)(5)(6)(7). Immune checkpoint inhibitors (ICIs), such as anti-programmed cell death 1 (PD-1) and programmed cell death-ligand 1 (PD-L1) agents, have considerably improved the survival of driver gene wild-type advanced NSCLC (8)(9)(10). Although a few reports have been published recently, the role of ICI in EGFR-mutant NSCLC after EGFR-TKI failure is still controversial. Disappointing results have been demonstrated with ICI monotherapy in IMMUNOTARGET (11) and other studies (12)(13)(14), while some physicians advocate that ICI-based combination therapy may be an option (15). Subgroup analysis in the IMpower 150 study showed that the combination of paclitaxel, carboplatin, bevacizumab, and atezolizumab improved PFS but not significant OS benefit as compared to that with bevacizumab plus chemotherapy. This four-drug regimen owned an incidence of grade 3 to 4 treatment-related adverse events of 57% (16). Two studies with a combination approach have reported promising results on response rate (RR) and survival (17,18), while flaws exist due to the small sample size and insufficient information on patients with T790M. Another study with ICI combination treatment got a worse outcome with an objective response rate (ORR) of 18.6% and a median progression-free survival (mPFS) of 2.8 months (19). Moreover, a few studies with small samples have retrospectively analyzed the data of EGFR 20 insertion mutation (EGFR 20Ins) to evaluate the efficacy of ICI (20)(21)(22). Therefore, more studies are urgent to explore the role of ICI in EGFR-mutant NSCLC patients.
This retrospective study aimed to summarize the efficacy of ICI in EGFR-mutant NSCLC after progression on TKI treatment and explore issues, such as the administration timing of ICI, whether ICI monotherapy or ICI-based combination therapy is better, and the efficacy of ICI for EGFR 20Ins. The inclusion criteria were as follows: treatment with ICI (anti-PD-1/PD-L1 inhibitor); a pathological diagnosis of NSCLC and at stage IV according to tumor size, lymph node, and metastasis (TNM) stages; exhibition the activation of EGFR mutations on exons 18 to 21. Patients who had participated in clinical trials or had other cancers were excluded. Related baseline demographic variables, including sex, age, Eastern Cooperative Oncology Group (ECOG) performance status, immunotherapy strategy, smoking history, sites of metastasis, histological type, and prior treatment information, were collected. This study adhered to the tenets of the Declaration of Helsinki and was performed following the principles of good clinical practice and approved by the institutional ethical review board. As only anonymous medical records of patients were used, the requirement for informed consent was waived by the ethical committee.

EGFR Mutation and PD-L1 Analysis
Tumor tissue samples obtained from biopsy, resection, and cytology were used for immunohistochemical detection. PD-L1 status was determined by immunohistochemistry analyses (23), and EGFR mutations were evaluated by polymerase chain reaction or next-generation sequencing (24), which was used according to standard protocols of the respective centers. The PD-L1 tumor proportion score (TPS) refers to the percentage of tumor cells showing partial or complete membrane staining (25). PD-L1 expression≥50% was classified as a strong positive result (26). All gene alterations and PD-L1 expression status were part of the patients' clinical information at baseline.

Statistical Analysis
Categorical variables are presented as numbers and percentiles, whereas continuous variables are presented as medians and ranges. Each patient's response to ICI treatment was assessed using the Response Evaluation Criteria in Solid Tumors (RECIST) v. 1

Clinical Features Associated With Outcomes in Patients With Common EGFR Mutations
All 96 patients with common EGFR mutations (19Del and L858R) had previously been treated with EGFR-TKIs. All patients with prior TKI treatment failure who carried the acquired T790M mutation have received osimertinib. Further analyses of clinical features were subsequently performed to identify the benefitting population. 46 patients were immediately administered ICI after progression on TKI, which was defined as front-line ICI post-TKI progression, whereas the remaining 50 patients received laterline ICI because they received other systemic therapy regimens in the interval between TKIs and ICI treatment. The patients who received front-line ICI showed enhanced survival benefits compared to those who received ICI as a later line post-TKIs progression (mPFS, 7 Figure 2). The group treated with front-line ICI had a better ECOG performance score and higher PD-L1 expression than the group treated with laterline ICI.
A total of 72 patients were treated with ICI-based combination therapy: 50 received a combination of ICI with chemotherapy, 8 received a combination of ICI with chemotherapy and radiotherapy, 12 received a combination of ICI with chemotherapy plus an antiangiogenic agent, and 2 received dual ICIs (an anti-PD-1 agent combined with an anti-cytotoxic-T-lymphocyte-associated protein 4 inhibitor). The efficacy of ICI-based combination therapy was better than that of ICI monotherapy (mPFS, 5 Figure 3).
A multivariate analysis was performed by including factors that were found to be significant in the univariate analysis (P<0.05) and those considered to be clinically significant ( Table 3). The results indicated that strongly positive PD-L1 expression (TPS≥50%), ICIbased combination therapy, front-line ICI treatment after EGFR TKI progression, and the EGFR L858R genotype were all significantly associated with improved PFS (P <0.05) ( Figure 5). A good ECOG status, ICI-based combination therapy, and frontline ICI treatment after EGFR TKI progression were found to be independently associated with a favorable OS, after adjusting for other clinical factors (P <0.05; Table 3).

DISCUSSION
Chemotherapy, as the most common subsequent treatment regimen after the discontinuation of EGFR-TKI therapy, has limited benefits for EGFR-mutant NSCLC patients (4-7). A retrospective study indicated that 27% of patients received chemotherapy combined with ICI after the failure of osimertinib     (17)(18)(19). The CT 18 study (18) and other studies using a combination approach of ICI with chemotherapy have exhibited survival benefits (16,17), which was also observed in our study, whereas a study with camrelizumab plus apatinib achieved inferior outcome (19). Basic studies support that chemotherapy, antiangiogenic drugs, and radiotherapy exert synergistic effects with ICI via positive regulation of the immune system, changing the tumor immune microenvironment, and releasing tumor neoantigens (28)(29)(30)(31)(32). Besides the role of ICI, the optimal combination strategy is still unclear. Our study including patients who received first-, second-, third-generation EGFR TKI in the first-line or after acquired T790M mutation reflected the real-world situation, and the majority of cases received ICI combined with chemotherapy. The current study evaluated the efficacy of ICI combination regimen versus monotherapy and observed improved survival from ICI-based combination therapy. Considering the toxicities of ICI combined with chemotherapy (16), an alternative combined    partner from chemotherapy to antiangiogenic drugs seems reasonable (19), but the efficacy of the chemotherapy-free combined strategy needed to be further explored. Several studies concerning gene wild-type NSCLC have indicated that the earlier the use of ICIs, the better the outcome maybe (33,34). Some studies on EGFR-mutant NSCLC after EGFR TKI failure recruited patients without prior palliative chemotherapy (17,18), whereas a study of camrelizumab plus apatinib (19) including patients in the later setting exhibited lower RR and shorter PFS. Our study showed that front-line administration of ICI after EGFR-TKI resistance was more beneficial in terms of PFS and OS. This phenomenon is consistent with that observed in patients with wild-type driver gene. Although the tumor microenvironment (TME) of EGFR-mutant NSCLC is immunosuppressive (28), EGFR-TKI may activate the TME by increasing dendritic cells and CD8+ cells, reducing Tregs, and inhibiting M2-like macrophages polarization at an early stage (35). EGFR-TKI could also affect the expression of PD-L1 (36) and the distribution of the CD4+, and Foxp3+ cells within the TME (37)(38)(39). We speculate that the insertion of other treatments before ICI may possibly perturb the favorable immune microenvironment that may exist after TKI treatment. Therefore, the administration timing of ICI treatment for this population may be also important.
The predictive effect of PD-L1 status on the efficacy of ICI treatment among EGFR-mutant NSCLC patients is inadequate and debatable. It is thought that the PD-L1 expression in EGFR-mutant NSCLC patients is mainly mediated by carcinogenic signaling pathways rather than an adaptive immune process, resulting in a lowered capacity to predict the efficacy of immunotherapy (40,41). Some studies have found that the status of PD-L1 expression could not be used to screen out ICI responders in EGFR-mutant NSCLC patients (42). On the contrary, other studies demonstrated that ICIs can also be used for EGFR-mutant NSCLC patients who have high PD-L1 expression (43). In cohort 1 (n=111) of the ALTLANTIC study (44), durvalumab was used as the third or later line treatment for advanced EGFR/ALK-positive NSCLC patients. Patients with PD-L1 expression ≥ 25% had an ORR of 12%, and better median PFS and 2-year OS rates than patients with PD-L1 expression < 25% (13.3 months vs. 9.9 months, 40.7% vs. 14.7%, respectively). Similarly, the results of our study indicated that PD-L1 expression ≥50% at baseline was related to better PFS of ICI treatment. EGFR L858R was found to be associated with favorable PFS in our study, which is consistent with the finding of a previous study (45).
It must be noted that this study has certain limitations. First, the results should be interpreted with caution because of the retrospective nature of the study. Second, PD-L1 expression data were not available for every individual. Finally, we could not obtain the PD-L1 expression status data after EGFR-TKI discontinuation, which may be more accurate to predict the efficacy of ICI treatment. Despite these limitations, this retrospective study was performed rigorously and ethically to provide a certain reference value for clinical practice.
In conclusion, ICI therapy, especially front-line ICI therapy and ICI-based combination therapy, may be beneficial for improving the prognosis of advanced EGFR-mutant NSCLC patients after EGFR-TKI therapy discontinuation. These findings need to be verified by prospective randomized controlled phase III clinical studies.

DATA AVAILABILITY STATEMENT
The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

ETHICS STATEMENT
The studies involving human participants were reviewed and approved by the institutional ethical review board. Written informed consent for participation was not required for this study in accordance with the national legislation and the institutional requirements.