Immunotherapy in Non-Small Cell Lung Cancer: Advancements and Challenges
The therapeutic paradigm for non-small cell lung cancer (NSCLC) has undergone a transformative shift over the past decade, driven by the advent of immune checkpoint inhibitors (ICIs) targeting the programmed death-1 (PD-1) and programmed death-ligand 1 (PD-L1) axis. These agents have demonstrated unprecedented long-term survival benefits in subsets of patients, redefining standard-of-care approaches across disease stages. However, challenges such as resistance mechanisms, biomarker limitations, and immune-related toxicities persist, necessitating further research to optimize clinical outcomes.
ICIs in First-Line Treatment of Advanced NSCLC
The KEYNOTE-024 trial marked a pivotal advancement, establishing pembrolizumab as a first-line monotherapy for advanced NSCLC with PD-L1 tumor proportion score (TPS) ≥50% and absence of EGFR/ALK alterations. Compared to platinum-based chemotherapy, pembrolizumab improved median progression-free survival (PFS) from 6.0 to 10.3 months (P < 0.001) and overall survival (OS) from 14.2 to 30.0 months (P = 0.002). Subsequent KEYNOTE-042 expanded these benefits to patients with PD-L1 TPS ≥1%, showing OS advantages (16.7 vs. 12.1 months; P = 0.0018). However, subgroup analysis revealed no significant OS benefit in patients with PD-L1 TPS 1–49%, suggesting that the survival advantage is predominantly confined to high PD-L1 expressors.
Combination strategies integrating ICIs with chemotherapy have emerged as a cornerstone for broader patient populations. Pembrolizumab combined with platinum-based chemotherapy gained approval for advanced squamous and nonsquamous NSCLC, irrespective of PD-L1 expression. In a phase III trial involving Chinese nonsquamous NSCLC patients, camrelizumab plus pemetrexed/carboplatin significantly improved objective response rate (ORR: 60.0% vs. 39.1%; P < 0.0001), PFS (11.3 vs. 8.3 months; P = 0.0002), and OS (not reached vs. 20.9 months; P = 0.0272) over chemotherapy alone. Similarly, atezolizumab combinations with carboplatin/nab-paclitaxel (IMpower130) or bevacizumab/carboplatin/nab-paclitaxel (IMpower150) demonstrated superior PFS and OS in nonsquamous NSCLC. These regimens underscore the synergistic potential of chemotherapy to enhance antigen release and T-cell activation, broadening the therapeutic reach beyond PD-L1 stratification.
ICIs in Early-Stage and Locally Advanced NSCLC
The PACIFIC trial revolutionized management of unresectable, locally advanced NSCLC by introducing durvalumab as consolidation therapy after definitive chemoradiotherapy. Durvalumab extended median PFS from 5.6 to 17.2 months and improved OS (median not reached vs. 29.1 months for placebo), establishing a new standard of care. This approach capitalizes on the immunogenic effects of radiation, which primes the tumor microenvironment for enhanced ICI activity.
In resectable early-stage NSCLC, neoadjuvant ICIs have shown promising feasibility. A pilot study of nivolumab in 21 patients achieved complete resection in 20 cases, with 45% exhibiting a major pathologic response (MPR ≤10% residual tumor). Subsequent trials exploring neoadjuvant PD-1/PD-L1 inhibitors alone or with CTLA-4 blockers or chemotherapy further validated this strategy. While MPR serves as a surrogate endpoint, its correlation with long-term survival remains under investigation in ongoing phase III trials. Adjuvant ICI therapy is also being evaluated in stage I–IIIA NSCLC, aiming to eradicate micrometastases post-resection.
Predictive Biomarkers: Beyond PD-L1
Despite the central role of PD-L1 expression in patient selection, its limitations are evident. Spatial-temporal heterogeneity, interassay variability, and discordance in immune cell scoring diminish its reliability. Tumor mutation burden (TMB) emerged as a complementary biomarker in CheckMate-227, where nivolumab/ipilimumab improved PFS (7.2 vs. 5.5 months; P < 0.001) and ORR (45.3% vs. 26.9%) in high TMB (≥10 mutations/megabase) patients. However, OS benefits were independent of TMB, highlighting the need for multimodal biomarker integration.
A combined analysis of T-cell-inflamed gene-expression profiles, PD-L1, and TMB demonstrated enhanced predictive accuracy, reflecting the complexity of tumor-immune interactions. Future strategies may incorporate dynamic biomarkers like circulating tumor DNA (ctDNA) to monitor treatment response and detect pseudoprogression.
Immune-Related Adverse Events and Clinical Management
ICIs are generally well-tolerated, but immune-related adverse events (irAEs) occur in 22% of patients (4% grade ≥3). Pneumonitis, colitis, and endocrine dysfunction are common, with fatal irAEs observed in 0.34% of cases, predominantly due to pneumonitis. Management relies on corticosteroids and immunosuppressive agents, guided by severity-based algorithms.
Notably, baseline corticosteroid use (≥10 mg prednisone equivalents) for cancer-related symptoms correlates with reduced ICI efficacy, whereas steroids for non-cancer indications (e.g., chronic obstructive pulmonary disease) do not compromise outcomes. This distinction emphasizes the need to minimize prophylactic steroids unless clinically imperative.
Hyperprogression and Pseudoprogression: Diagnostic Dilemmas
Hyperprogressive disease (HPD), characterized by accelerated tumor growth during ICI therapy, affects 9–20% of advanced NSCLC patients, with a median OS of 3.4 months. Risk factors include age >65 years, EGFR mutations, MDM2/4 amplifications, and STK11 alterations. In contrast, pseudoprogression—initial radiographic progression followed by response—occurs in 5% of cases, necessitating immune-specific criteria (iRECIST) and ctDNA monitoring to differentiate from true progression.
Overcoming Resistance to ICIs
Primary resistance arises from “cold” tumor phenotypes lacking T-cell infiltration or immunosuppressive microenvironments rich in TGF-β, VEGF, or regulatory T cells. Strategies to convert cold tumors include combining ICIs with chemotherapy, radiotherapy, or agents targeting inhibitory pathways (e.g., TIM-3, LAG-3). For altered-excluded tumors, therapies to enhance T-cell trafficking (e.g., CXCR4 inhibitors) or disrupt stromal barriers (e.g., FAK inhibitors) are under investigation.
Acquired resistance involves adaptive immune escape mechanisms, such as loss of antigen presentation or upregulation of alternative checkpoints. Dual checkpoint blockade (e.g., PD-1/CTLA-4 inhibitors) and novel combinations with metabolic modulators or vaccines represent promising avenues to restore sensitivity.
Future Directions
The integration of ICIs into NSCLC treatment has yielded remarkable progress, yet challenges remain. Personalized biomarker-driven approaches, rational combination therapies, and advanced diagnostic tools (e.g., AI-based imaging, multi-omics profiling) are critical to overcoming resistance and optimizing patient selection. Ongoing research into neoadjuvant and adjuvant settings, as well as novel immune targets, holds promise for further improving survival outcomes in this historically lethal malignancy.
doi.org/10.1097/CM9.0000000000001338
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