Comparative effectiveness of pembrolizumab-chemotherapy versus chemotherapy with/without bevacizumab in unresectable, locally advanced or metastatic non-small cell lung cancer: a Chinese multicenter real-world analysis emphasizing PD-L1-negative populations

Introduction

Immune checkpoint inhibitors (ICIs) have revolutionized the treatment of non-small cell lung cancer (NSCLC) and greatly improved patient prognosis. Programmed death protein 1 (PD-1) inhibitors and programmed cell death ligand 1 (PD-L1) inhibitors interrupt the PD-1/PD-L1 signaling pathways, stimulating T-cell activation and enhancing tumor cell recognition and elimination (1). Nonetheless, not all patients benefit from ICIs, and the PD-L1 tumor proportion score (TPS), which represents the number of tumor cells expressing PD-L1, is important. A PD-L1 TPS <1% indicates the absence of PD-L1 in tumor cells, and may hinder immune cell activation and infiltration in the tumor microenvironment, affecting the efficacy of ICIs. Notably, a significant proportion of NSCLC patients exhibit negative PD-L1 expression. The KEYNOTE-189 and KEYNOTE-407 studies reported that 30.8% and 34.7% of patients had PD-L1 TPS <1%, respectively (2,3). While real-world observations have documented rates as high as 41–57% (4). The efficacy of monotherapy with ICIs is often limited in these patients compared to those with PD-L1 TPS ≥1%. However, combining chemotherapy and ICIs can enhance anti-tumor immunity by releasing tumor antigens during chemotherapy-induced tumor lysis, boosting the immune response (5).

An exploratory pooled analysis was conducted using individual data from the global KEYNOTE-189 and Japanese extension studies of patients with metastatic non-squamous NSCLC without epidermal growth factor receptor (EGFR) or anaplastic lymphoma kinase (ALK) alterations, and the KEYNOTE-407 global and Chinese studies of patients with metastatic squamous NSCLC (6). The results revealed that patients with PD-L1 TPS <1% [immunohistochemistry (IHC), Daco 22c3 antibody, which was utilized to assess the level of PD-L1 expression in the KEYNOTE-189 and KEYNOTE-407 trials] who received pembrolizumab plus platinum-based dual chemotherapy had a significantly better progression-free survival (PFS) time of 6.5 months and an overall survival (OS) time of 18.3 months than those in the control group who did not receive pembrolizumab [PFS: 5.5 months, hazard ratio (HR) =0.66, 95% confidence interval (CI): 0.54–0.81; OS: 11.4 months, HR =0.64, 95% CI: 0.51–0.79], as well as better OS and PFS times than patients in the ECOG 4599 trial who received chemotherapy plus bevacizumab (PFS: 6.2 months; OS: 12.3 months) (6,7).

Consequently, pembrolizumab plus chemotherapy is a standard-of-care first-line therapy for patients with PD-L1 TPS <1%. However, information on patients negative for PD-L1 comes primarily from subgroup analyses of phase-III randomized controlled trials; none of which were designed specifically for this group. ICI plus chemotherapy has been shown to extend PFS and OS to varying degrees; however, the HRs for OS were 0.83 in the KEYNOTE-407 trial and 0.81 in the IMPOWER-130 trial, with a 95% CI across 1 (2,3,8-11). Further, a real-world study by Bailey et al. reported that up to 62.4% of this population received first-line chemotherapy only (12), emphasizing the urgent need for further research on ICI effectiveness in negative PD-L1 patients.

This real-world study aimed to analyze the efficacy, adverse events (AEs), and prognostic factors of chemotherapy plus pembrolizumab in NSCLC patients with PD-L1 TPS <1%, and unresectable, locally advanced, or metastatic disease. We present this article in accordance with the STROBE reporting checklist (available at https://tlcr.amegroups.com/article/view/10.21037/tlcr-2025-271/rc).

Methods

Study population

We retrospectively reviewed the data of patients treated at the Peking Union Medical College Hospital (PUMCH) between December 2017 and April 2024. Patients’ medical profiles were retrieved from a real-world electronic medical database (CAPTRA-Lung database) (13). To be eligible for inclusion in the study, the patients had to meet the following inclusion criteria: (I) aged 18 years or older; (II) have histologically diagnosed NSCLC and unresectable, locally advanced (the diagnosis was established by a multidisciplinary team comprising specialists in lung oncology, thoracic surgery, radiation therapy, and medical imaging), or metastatic disease; (III) have non-squamous cell lung cancer (non-SCC) without the sensitive EGFR or ALK or proto-oncogene receptor tyrosine kinase (ROS1) alterations; genetic testing was optional for patients with SCC; (IV) have received at least one cycle of pembrolizumab plus chemotherapy (the Pembro group), or platinum-based dual chemotherapy (the Chemo group); the SCC patients received paclitaxel plus platinum; the non-SCC patients received pemetrexed plus platinum and bevacizumab (the treatment regimens were selected based on the first-line recommendations for different pathological subtypes before immunotherapy was approved for NSCLC indications and a thorough assessment of the patient’s condition and preferences); and (V) have PD-L1 TPS <1% before treatment if in the Pembro group. Patients were excluded from the study if they met any of the following exclusion criteria: (I) had incomplete baseline data; (II) had previously used any ICIs before first-line therapy (these excluded patients predominantly received ICIs in the following clinical contexts: perioperative use of ICIs or maintenance therapy with ICIs following concurrent or sequential chemoradiotherapy for locally advanced disease); and (III) had received chemotherapy combined with anti-tumor regimens other than pembrolizumab or bevacizumab.

The data for patients that met the criteria for the Pembro group were provided by the Beijing Cancer Hospital, Beijing Chest Hospital, The Second Affiliated Hospital of Nanchang University, and The Fourth Hospital of Hebei Medical University. This study was conducted in accordance with the ethical principles of the Declaration of Helsinki and its subsequent amendments. Ethical approval was granted by the Ethics Committee of PUMCH (approval No. JS-1410). All patients included in this study had provided written informed consent prior to enrollment and were subsequently registered in the CAPTRA-Lung study database. All participating hospitals/institutions were informed and agreed with this study. Figure 1 shows a flowchart of the study design.

Figure 1 Patient selection flowchart. ALK, anaplastic lymphoma kinase; EGFR, epidermal growth factor receptor; ICIs, immune checkpoint inhibitors; SCC, squamous cell lung cancer; NSCLC, non-small cell lung cancer; PD-L1, programmed cell death ligand 1; ROS1, proto-oncogene receptor tyrosine kinase; TPS, tumor proportion score.

Clinical data collection

The demographic characteristics and therapeutic data of the patients, including sex, age, smoking history, histological subtype, stage, metastatic sites, Eastern Cooperative Oncology Group-Performance Status (ECOG-PS), PD-L1 TPS results, treatment details, response evaluation, PFS, OS, and AEs, were collected. The most recent follow-up was conducted on August 16, 2024. All patients were contacted by telephone to assess their survival status and ascertain mortality dates. The absence of a specified endpoint at the final follow-up indicated censoring.

PD-L1 analysis

The PD-L1 analysis was performed at each center according to the local procedures. The antibodies used in the Pembro group were 22C3 (94.7%), SP263 (4.4%), and 28-8 (0.88%). While 28% of patients in the Chemo group were evaluated for PD-L1 expression using the Dako 22C3 antibody, PD-L1 assessment was not performed for the remaining patients.

Assessment

The objective response rate (ORR) and disease control rate (DCR) were evaluated according to the Response Evaluation Criteria in Solid Tumors (version 1.1). The PFS and OS times were calculated from the initiation of pembrolizumab or chemotherapy until disease progression or death. The AEs were recorded and graded according to the Common Terminology Criteria for Adverse Events (version 5.0).

Statistical analysis

The Chi-squared test or Fisher’s exact test was used to assess rate differences. The Student’s t-test or the Mann-Whitney U test was used for the continuous variables. When dichotomization of continuous variables was necessary for analysis, the median value served as the cut-off point to mitigate skewness effects and enhance clinical utility. The median follow-up time was estimated using the reversed Kaplan-Meier method. The survival analysis was performed using the Kaplan-Meier method. The log-rank test was used to compare the survival curves, and the corresponding 95% CIs were calculated. The effects and influencing factors were analyzed using the Cox proportional hazards model. Multivariate analyses were performed after adjusting for age, sex, smoking status, histological subtype, and disease stage. To examine the interaction effects between subgroup variables and treatment measures, interaction terms were constructed by incorporating each subgroup variable with the treatment group into the model separately. The significance of these interactions was then assessed using the Wald test to calculate the corresponding P values. The Cox proportional hazards regression model was used to analyze the variables correlated with PFS and OS in the Pembro group. Variables with a P value <0.1 in the univariate regression analysis were included in the multivariate regression model. Missing data were not imputed and were instead excluded from the analysis. Statistical significance was defined as a two-sided P value <0.05. All the statistical analyses were performed using SPSS (version 29.0, IBM Corporation; Armonk, NY, USA) or ZStats V0.9.1 (https://www.zstats.net).

Results

Patient characteristics

In total, 2,250 patients with stage III–IV NSCLC and 1,017 patients with no sensitive EGFR, ALK or ROS1 alterations who had not previously used ICIs and who received first-line chemotherapy therapy were identified. After screening, 99 patients from PUMCH and 15 eligible patients from the four other centers were included in the Pembro group, and 132 patients were included in the Chemo group. The baseline clinical features of the patients are shown in Table 1. The patients were all Asians. The Chemo group patients had a younger median age than the Pembro group patients (63 vs. 66 years), but their other characteristics were similar. In the overall population, most of the patients (78.5%) were male, were former or current smokers (70.7%), had non-SCC (64.6%), had stage IV cancer (84.6%), and had an ECOG-PS score of 0–1 (94.3%). At the baseline, 13.4%, 10.6%, 28.9%, and 9.3% of the patients had brain, liver, bone, and adrenal metastases, respectively. The baseline features according to the pathological subtype and treatment are summarized in Table 2.

Genetic mutations

EGFR, ALK and ROS1 alterations were detected in the non-SCC patients in both treatment groups, but no sensitive alterations were detected. In the Pembro group, 98.6% (73/74) of the patients underwent Kirsten rat sarcoma viral antigen (KRAS) gene detection; while in the Chemo group, 69.4% (59/85) of the patients underwent KRAS gene detection. The mutation carriage rates were similar between the Pembro and Chemo groups [27.4% (20/73) and 27.1% (16/59), respectively). The most prevalent mutation types were KRAS G12C and G12V. The genes that were mutated more than twice in any treatment group are listed in Table 3.

Efficacy

ORR

At the data cut-off date, the median follow-up time was 28.3 (95% CI: 24.0–32.6) months in the overall population, 26.0 (95% CI: 20.4–31.6) months in the Pembro group, and 29.9 (95% CI: 17.4–42.4) months in the Chemo group. The median and interquartile range (IQR) of pembrolizumab cycles was 6 (IQR, 3–14) in the Pembro group, 4 (IQR, 3–6) for the SCC patients in the Chemo group, and 6 (IQR, 4–10) for the non-SCC patients in the Chemo group. The ORR of the Pembro group (39.5%, 45/114) was higher than that of the Chemo group (28.0%, 37/132; P=0.007), and the ORR of the SCC patients in the Pembro group was higher (52.5%, 21/40) than that of the non-SCC patients (32.4%, 24/74, P=0.04,) in the Pembro group and the SCC patients in the Chemo group (31.9%, 15/47; P=0.052) (Figure 2A). The DCRs were similar [85.1% (97/114) vs. 84.1% (111/132); P=0.86] between the Chemo group and the Pembro group (Figure 2B).

Figure 2 The efficacy in different populations. (A) The objective response rates; (B) the disease control rates. Chemo, chemotherapy; DCR, disease control rate; ORR, objective response rate; pembro, pembrolizumab; SCC, squamous cell lung cancer.

PFS

At the data cut-off date, disease progression in the Pembro group (64.0%, 73/114) was comparable to that in the Chemo group (65.9%, 87/132), and these groups had median PFS time of 9.5 (95% CI: 7.5–11.5) and 7.2 (95% CI: 5.7–8.7) months, respectively (HR =0.64, 95% CI: 0.46–0.87; P=0.004, Figure 3A). The PFS times were 9.3 (95% CI: 7.6–11.0) and 8.0 (95% CI: 6.0–10.0) months for the non-SCC patients in the Pembro and Chemo groups, respectively (HR =0.89, 95% CI: 0.61–1.31; P=0.56, Figure 3B), and 13.8 (95% CI: 3.2–24.1) and 4.8 (95% CI: 3.4–6.2) months for the SCC patients in the Pembro and Chemo groups, respectively (HR =0.31, 95% CI: 0.17–0.58; P<0.001, Figure 3C).

Figure 3 PFS of all patients (A), patients with non-SCC (B), and patients with SCC (C) in the different treatment groups, as well as forest plots for some key subgroups (D). Chemo, chemotherapy; CI, confidence interval; ECOG-PS, Eastern Cooperative Oncology Group-Performance Status; HR, hazard ratio; n, number; PFS, progression-free survival; pembro, pembrolizumab; SCC, squamous cell lung cancer; y, years.

A subgroup analysis of the PFS outcomes between the two groups was performed (Figure 3D). The Pembro group demonstrated PFS benefits across the majority of subgroups, including patients aged <65 or ≥65 years, and those with stage III or IV disease, regardless of adrenal metastasis status, male patients, smokers, individuals with an ECOG-PS of 0–1, those with <3 distant metastatic sites, and subgroups without liver, brain, or bone metastases, as well as those with SCC.

The PFS of the non-SCC patients in the Pembro group with the KRAS mutations (KRASm) (12.9 months, 95% CI: 5.4–20.4 months) was longer than that of those with wild-type KRAS gene (8.8 months, 95% CI: 6.4–11.2 months) (Figure S1A); however, this difference was not statistically significant (HR =0.56, 95% CI: 0.29–1.08; P=0.08).

OS

At the data cut-off date, the patient mortality rate was lower in the Pembro group (45.6%, 52/114) than in the Chemo group (61.4%, 81/132), and these groups had median OS times of 21.2 (95% CI: 16.0–26.4) months in the Pembro group and 20.1 (95% CI: 15.5–24.7) months in the Chemo group, respectively (HR =0.71, 95% CI: 0.50–1.00; P=0.052, Figure 4A) and the corresponding estimated OS rates at 24 months were 46.4% (95% CI: 35.6–57.2%) and 39.9% (95% CI: 30.3–49.5%). The OS times were 18.1 (95% CI: 13.4–22.8) months and 21.3 (95% CI: 18.3–21.3) months for the non-SCC patients in the Pembro and Chemo groups, respectively (HR =1.0, 95% CI: 0.65–1.54; P=0.99, Figure 4B) and the corresponding estimated OS rates at 24 months were 40.6% (95% CI: 27.3–53.9%) and 42.7% (95% CI: 30.7–54.7%), respectively. The OS times were not reached (95% CI: NR–NR) and 14.2 (95% CI: 6.3–22.1) months for the SCC patients in the Pembro and Chemo groups, respectively (HR =0.42, 95% CI: 0.22–0.78, P=0.007, Figure 4C) and the corresponding estimated OS rates at 24 months were 56.1% (95% CI: 38.3–73.9%) and 38.8% (95% CI: 22.3–55.3%), respectively.

Figure 4 OS of all patients (A), patients with non-SCC (B), and patients with SCC (C) in the different treatment groups, as well as forest plots for some key subgroups (D). Chemo, chemotherapy; CI, confidence interval; ECOG-PS, Eastern Cooperative Oncology Group-Performance Status; HR, hazard ratio; n, number; NR, not reached; OS, overall survival; pembro, pembrolizumab; SCC, squamous cell lung cancer; y, years.

The subgroup analysis of the OS between the groups showed that the OS benefit of pembrolizumab was consistent across most groups (Figure 4D). However, the Kaplan-Meier curves did not distinguish between patients with or without the KRASm in the Pembro group (Figure S1B).

The second-line treatment options available for patients with disease progression are detailed in Figure S2. In the Chemo group, 34.5% of the patients received immune-based therapy as a second-line treatment.

Cox proportional hazard regression model for PFS and OS in the Pembro group

The univariate Cox proportional regression results for PFS and OS are presented in Tables S1,S2. The multivariate Cox model (Model 1) for PFS indicated that immune-related adverse events (irAEs) and an age <65 years were significant protective factors for disease progression (Figure 5A). The multivariate Cox model (Model 1) for OS indicated that irAEs, SCC, and an ECOG-PS score <2 were protective factors for mortality, while smoking and an age ≥65 years were risk factors for mortality (Figure 5B).

Figure 5 Forest plots of multivariate Cox proportional hazard ratio for PFS (A) and OS (B) in the Pembro group. CI, confidence interval; ECOG-PS, Eastern Cooperative Oncology Group-Performance Status; HR, hazard ratio; irAEs, immune-related adverse events; OS, overall survival; PFS, progression-free survival; SCC, squamous cell lung cancer; y, years.

Because some patients were missing baseline routine blood and serum albumin data, we performed another Cox hazard regression analysis to conduct exploratory analysis of PFS and OS (Model 2), incorporating the neutrophil-to-lymphocyte ratio (NLR), prognostic nutritional index (PNI), and platelet-to-lymphocyte ratio (Figure S3). A NLR <3.95 (HR =0.49, 95% CI: 0.24–0.99), and an ECOG-PS score of 0–1 (HR =0.39, 95% CI: 0.15–0.99) were protective factors for mortality in Model 2.

Safety

Treatment-related AEs not recorded as irAEs (i.e., non-irAEs) were observed in 96.3% (105/109) of the patients in the Pembro group and 95.2% (118/124) of the patients in the Chemo group. Non-irAEs with an incidence of ≥5% and all irAEs are detailed in Table 4. Grade 3–4 non-irAEs had an incidence rate of 46.8% (51/109) in the Pembro group and 33.1% (41/124, P=0.03) in the Chemo group; the highest rates were observed for leukopenia (31.2%) or neutrophilia (28.2%), followed by anemia and thrombocytopenia.

In the Pembro group of 45 patients, 63 irAEs involving multiple organs or systems were reported. Thyroid dysfunction occurred in 14.0% of the patients, rash/itch in 10.5%, and checkpoint inhibitor pneumonitis (CIP) in 7.0%. Among grade ≥3 irAEs, four cases of rash (one grade 4 and three grade 3) occurred, with onset intervals ranging from 11 to 202 days post-pembrolizumab initiation. Three patients with severe rash achieved complete resolution following systemic glucocorticoids. Four patients developed grade 3 CIP, with onset between 37 days and >2 years (including one delayed-onset case 2 months post-treatment cessation). All CIP patients discontinued pembrolizumab and received glucocorticoids, with two requiring escalation therapy: one refractory case responded to adjunctive tocilizumab (interleukin-6 receptor antagonist), while another received combined tocilizumab and ruxolitinib (a selective inhibitor of Janus kinase). One patient experienced grade 4 myocarditis after the first cycle, managed via pembrolizumab withdrawal, pulsed methylprednisolone (1 g/day ×3 days), sequential biologics (tocilizumab, ruxolitinib and cyclosporine), and supportive care, achieving partial response but persistent cardiac dysfunction (New York Heart Association class III). The grade 3–4 irAEs with the highest incidence rates were rashes (3.5%) and CIP (3.5%), followed by increased creatinine levels, adrenal insufficiency, colitis, diabetes mellitus, and myocarditis. No grade 5 irAEs or new irAEs were observed.

Discussion

This retrospective study reviewed the efficacy of first-line pembrolizumab plus chemotherapy in patients with unresectable, locally advanced or metastatic PD-L1-negative NSCLC. The patients in the Pembro group had median PFS and OS time of 9.5 and 21.2 months, respectively, and an ORR of 39.5%. Compared to the Chemo group, the Pembro group showed a significant reduction of 36% in the risk of disease progression, and of 29% in the risk of mortality, and had a significantly improved ORR. In the Pembro group, male patients, smokers, and patients with SCC had better survival outcomes. The exploratory analysis revealed that the SCC patients had the highest PFS and OS. In the non-SCC patients negative for PD-L1 expression, there was no significant difference in PFS or OS between the Pembro group and the Chemo group. The patients with irAEs had a 49% lower disease-progression risk and a 51% lower mortality risk. Age ≥65 years was unfavorable in terms of both PFS and OS. The Pembro group had a greater incidence of AEs, and the common irAEs involved the thyroid and skin; no new irAEs were reported.

For the PD-L1-negative subgroups in the KEYNOTE-189 and 407 studies, the median PFS and OS times were 5.1 and 10.2 months (non-SCC), and 5.5 and 11.0 months (SCC) in the Chemo group, respectively, compared with 6.2 and 17.2 months (non-SCC), and 6.3 and 15.0 months (SCC) in the Pembro group (2,3). The pooled analysis also showed that pembrolizumab significantly lengthened the PFS and OS times (6). Our analysis confirmed these findings; however; the PFS and OS times in our study were superior to those reported in the pooled analysis. A real-world study of 22 centers in Argentina reported PFS and OS medians of 10.0 and 20.8 months in PD-L1-negative NSCLC patients who received immunotherapy (14), which is consistent with our analysis. The longer PFS reported in the real-world results (compared to the pooled analysis) might be attributed to various factors causing disparate responses to immunotherapy, including racial and regional variations, diverse smoking conditions, gene mutations, and co-mutations. In addition, our study included patients with stage III disease, while the proportion of stage IV patients with liver metastases decreased from 13.7% in the pooled analysis to 8.8% in the Pembro group of our study (6). An extended follow-up period is needed to obtain more survival data.

The results of the pooled analysis and our study showed that the SCC patients treated with pembrolizumab plus chemotherapy had a significantly higher ORR and improved survival outcomes compared to chemotherapy despite negative PD-L1 expression (6). The pronounced clinical benefit of immunotherapy observed in SCC patients compared to non-squamous NSCLC may be driven by distinct biological features. First, SCC tumors frequently exhibit a higher tumor mutational burden (TMB) and TP53 mutation rates, likely attributable to genomic instability caused by smoking. Second, the SCC immune microenvironment is often characterized by increased infiltration of CD8⁺ T cell creating a pro-inflammatory milieu that favors immune checkpoint activation. These might explain why SCC showed greater immune advantages (15-18). A further analysis of these factors is needed.

Before the immunotherapy era, trials, including ECOG4599 (PFS: 6.2 vs. 4.5 months; OS: 12.3 vs. 10.3 months) and AVAIL (PFS: 6.5–6.7 vs. 6.1 months), endorsed bevacizumab combined with chemotherapy as a first-line therapy for advanced non-SCC patients harboring no driver genes (7,19). ICIs have revolutionized the treatment landscape of lung cancer. However, whether pembrolizumab combined with chemotherapy provide incremental benefit over bevacizumab plus chemotherapy in PD-L1-negative non-SCC remains an unresolved clinical question, particularly given the heterogeneous outcomes observed across trials. For instance, in the PD-L1-negative subgroup analysis of the IMPOWER150 trial, which compared the efficacy of chemotherapy combined with atezolizumab [atezolizumab-carboplatin-paclitaxel (ACP)] or chemotherapy plus bevacizumab [bevacizumab-carboplatin-paclitaxel (BCP)], or a four-drug combination [chemotherapy plus atezolizumab and bevacizumab, atezolizumab-bevacizumab-carboplatin-paclitaxel (ABCP)], neither the ACP nor ABCP arms showed significantly lengthened PFS or OS compared to the BCP arm (20). Similarly, Wang et al. performed a retrospective analysis of 105 advanced non-SCC patients who underwent first-line chemotherapy combined with ICIs or BCP, and found no significant differences in PFS (6.5 vs. 6.2 months; P=0.38) and OS (15.6 vs. 17.9 months; P=0.57) in the PD-L1 TPS <1% subgroup (21). Our findings are consistent with these results.

Predicting ICI efficacy is both crucial and challenging. Various factors, including demographic characteristics, genetic backgrounds, the immune microenvironment, liquid biopsy assessment, and irAEs, may affect ICI efficacy. Our study found a correlation between PFS and irAEs. Although the precise mechanisms by which irAEs occur have not been fully elucidated, they probably represent bystander effects from activated T-cells and are consistent with the known mechanism of action of ICIs (22). Grangeon et al. reported that advanced NSCLC patients experiencing irAEs had better PFS and OS, and a higher ORR (23). Teraoka et al. reported that irAE occurrence within six weeks of nivolumab use was linked to an improved ORR and prolonged PFS (24). Moreover, a recent retrospective multicohort study of 39,258 patients examined the relationship between irAEs affecting different organs and prognosis. Patients with endocrine-related irAEs (HR =0.53, 95% CI: 0.40–0.70; P<0.001) or cutaneous irAEs (HR =0.61, 95% CI: 0.46–0.81; P<0.001) had better survival outcomes at the 6-month time point; while patients experiencing respiratory-type irAEs had worse survival outcomes at the 6-month time point (HR =1.60, 95% CI: 1.25–2.03; P<0.001) (25). These findings emphasize the need for individualized management strategies targeting specific groups of irAEs in clinical practice.

Gene mutation status is correlated with ICI efficacy. KRASm is a prevalent driver gene for NSCLC in Western patients, and ranks second to EGFR mutations in Asian patients (26). In the chemotherapy era, KRASm has served as a prognostic biomarker for poor outcomes in NSCLC (27). However, in the immunotherapy era, the prognostic significance of KRASm remains controversial. Patients with KRASm are more likely to exhibit high PD-L1 expression (28). Another real-world study found that 32.4% of patients with KRASm had negative PD-L1 expression and a greater proportion of co-mutated STK11 and KEAP1 genes. These co-mutations may create an immunosuppressive microenvironment that influences immunotherapy outcomes. In this study, the PD-L1-negative patients with KRASm exhibited 1.23-fold and 1.46-fold increased risks of disease progression and mortality, respectively, compared to those without KRASm. The prognosis of patients harboring these co-mutations was even worse (29). Liu et al. reported that KRAS G12D is associated with primary resistance to ICIs (30). The co-mutation of KRAS G12C and TP53 alteration is correlated with an improved response to immunotherapy (31,32). These results suggest that the correlation between KRASm and ICI efficacy is complex. In our study, patients with negative PD-L1 and KRASm expression had better PFS. However, because of the limited sample size, it remains unclear whether KRAS/STK11/KEAP1 mutations have predictive or prognostic value in patients negative for PD-L1 and can guide treatment choices. The prognostic effect of KRASm requires consideration of the PD-L1 status, mutant subtypes, co-mutations, and treatment options.

Some serum inflammatory markers and nutritional indices are associated with ICI efficacy and prognosis. Takada et al. analyzed 226 patients with advanced NSCLC, and reported that an absolute neutrophil count/(white blood cell concentration − absolute neutrophil count) ≥2.79 was linked to shorter PFS and OS, independent of PD-L1 expression (33). In addition, a meta-analysis of 1,359 NSCLC patients treated with ICIs revealed that a lower baseline PNI was associated with a shorter PFS and OS (34). Shoji et al. refined the predictive effect of PNI independent of PD-L1 expression, showing that lower PNI levels were correlated with worse OS outcomes (35). Our Model 2 for OS found that patients with a NLR <3.95 had better OS, which suggests that it could be a valuable biomarker for the prognostic assessment of PD-L1-negative NSCLC immunotherapy.

Limitations

This study has several limitations. First, this was a retrospective study with a small sample size and sensitivity analyses were not performed as such analyses risked further reducing statistical power and producing unstable estimates. While multivariable adjustments were rigorously applied to address measurable confounders, the potential impact of unmeasured confounding or methodological assumptions on the results cannot be fully excluded. Future large-scale studies with expanded cohorts are warranted to validate the robustness of these findings and explore additional sensitivity scenarios. Second, because of economic and time constraints, and an insufficient sample size, PD-L1 status was not assessed in all patients in the Chemo group. The PFS time of the patients receiving chemotherapy alone were 4.2, 6.0, and 5.9 months for the PD-L1 TPS ≥50%, 1–49%, and <1% subgroups, respectively, in the KEYNOTE-407 trial, and 4.8, 4.9, and 5.1 months for the PD-L1 TPS ≥50%, 1–49%, and <1% subgroups, respectively, in KEYNOTE-189 trial. Considering these results and the ICI mechanisms of action, we conclude that PD-L1 expression had little effect on chemotherapy efficacy. Third, the treatment groups differed in several baseline characteristics, including age, histology, and access to PD-L1 testing: (I) while patients in the Chemo group were younger than those in the Pembro group, our multivariate Cox regression revealed a significant interaction between age and treatment effect. Specifically, younger patients (<65 years) receiving pembrolizumab-chemotherapy demonstrated superior survival benefits. This suggested the observed age imbalance may amplify rather than diminish the clinical validity of our findings. (II) Our histology-stratified analysis revealed baseline smoking history imbalances in both SCC and non-SCC. This systemic mismatch likely stemmed from the absence of PD-L1 screening in the Chemo group, given the established association between smoking exposure and elevated PD-L1 expression (36). While these imbalances cannot be fully eliminated in observational studies, we mitigated their impact through multivariable Cox regression adjusting for histological subtype. (III) We acknowledged that 5.3% of PD-L1 tests used alternative antibodies (SP263/SP142). However, 94.7% employed the Daco 22C3 assay, and all results were interpreted using the validated TPS system. A recent multicenter validation study had demonstrated 83–92% concordance between 22C3 and SP263 assays in NSCLC, substantially reducing methodological heterogeneity concerns (37). Finally, despite efforts to standardize treatment protocols, inherent variability in PD-L1 assay platforms, supportive care practices, and institutional treatment cultures across centers may introduce unmeasured confounding. Future studies incorporating centralized biomarker testing and prospective trial designs are warranted to validate these findings.

Conclusions

In a real-world dataset, pembrolizumab plus chemotherapy may improve the PFS and OS of the PD-L1 negative patients with unresectable, locally advanced, or metastatic NSCLC, and had manageable toxicity. SCC, smoking, and male sex showed the greatest benefits. The occurrence of irAEs was associated with a potential therapeutic benefit from pembrolizumab; patients aged ≥65 years showed increased disease progression and poorer OS than those of younger age in the Pembro group.

Acknowledgments

We would like to thank Editage (www.editage.cn) for the English language editing.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://tlcr.amegroups.com/article/view/10.21037/tlcr-2025-271/rc

Data Sharing Statement: Available at https://tlcr.amegroups.com/article/view/10.21037/tlcr-2025-271/dss

Peer Review File: Available at https://tlcr.amegroups.com/article/view/10.21037/tlcr-2025-271/prf

Funding: This work was supported by the National High Level Hospital Clinical Research Fund (No. 2022-PUMCH-A-128 to Y.X.; No. 2022-PUMCH-B-106 to M.W.; and No. 2022-PUMCH-C-054 to W.Z.) and the Capital’s Funds for Health Improvement and Research (No. 2022-2Z-4017 to Y.X.).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tlcr.amegroups.com/article/view/10.21037/tlcr-2025-271/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. This study was conducted in accordance with the ethical principles of the Declaration of Helsinki and its subsequent amendments. Ethical approval was granted by the Ethics Committee of PUMCH (approval No. JS-1410). All patients included in this study had provided written informed consent prior to enrollment and were subsequently registered in the CAPTRA-Lung study database. All participating hospitals/institutions were informed and agreed with this study.

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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