PD-L1 Testing in Lung Cancer: Are We Chasing the Wrong Target?
"Unraveling the complexities of PD-L1 as a biomarker for NSCLC treatment and exploring more reliable alternatives for personalized immunotherapy."
Immunotherapy, particularly treatments targeting programmed cell death-1 (PD-1) and programmed cell death ligand-1 (PD-L1), has revolutionized the management of advanced non-small cell lung cancer (NSCLC). These therapies have become standard options in both initial and subsequent lines of treatment. While some patients experience lasting benefits, with 10-20% showing durable responses, identifying who will truly benefit remains a significant challenge.
PD-L1 expression, measured in tumor cells, has been used to predict responses to immune checkpoint inhibitors. However, its effectiveness as a biomarker has been inconsistent. Some studies show a correlation between PD-L1 levels and treatment success, while others do not. This inconsistency has led researchers to seek more reliable biomarkers to guide immunotherapy decisions.
This article examines the complexities of using PD-L1 as a biomarker in NSCLC, discusses the limitations that complicate its use, and explores promising alternative biomarkers currently under investigation. By understanding these challenges and emerging options, clinicians can move closer to personalized immunotherapy strategies for NSCLC.
Current Role of PD-L1 Testing
For advanced non-small cell lung cancer (NSCLC) without driver mutations, immune checkpoint inhibitors combined with chemotherapy are described as standard first-line therapy, while PD-L1 remains the only approved immunotherapy marker. A 2023 analysis combined clinical-trial and real-world data to assess the predictive and prognostic value of biomarkers for checkpoint-inhibitor outcomes in NSCLC. Real-world research has also examined pembrolizumab prescribing patterns among patients with PD-L1-high NSCLC treated between June 2019 and June 2021.
Standard Testing, Variable Results
PD-L1 testing is described as standard for patients with NSCLC, although results can vary between testing approaches. The College of American Pathologists guideline highlights both the clinical rationale for PD-L1 and tumor mutational burden testing and the technical challenges of PD-L1 testing and interpretation. Real-world studies are also examining how clinical, demographic, and socioeconomic characteristics shape first-line treatment patterns in metastatic NSCLC.
From Checkpoint Biology to Biomarker Testing
Checkpoint inhibition has dramatically altered the treatment landscape for NSCLC, a historically treatment-resistant malignancy. Reviews of PD-L1 as a biomarker emphasize that pre-analytical and analytical factors, scoring algorithms, and the site and timing of tissue acquisition can influence test results. Research discussed in relation to the CheckMate-227 and IMpower 150 trials also identified potential biomarkers that, if confirmed prospectively, could broaden prediction of immunotherapy outcomes beyond PD-L1.
Why PD-L1 Isn't Always the Answer: Understanding the Biomarker Puzzle
Several factors contribute to the challenges of using PD-L1 as a reliable biomarker:
- Tissue Collection Timing: When the sample is taken can affect PD-L1 levels.
- Antibodies and Methods: Different tests use different antibodies and scoring systems, leading to inconsistent results.
- Test Design: Lack of standardized test designs makes comparing results across studies difficult.
Quantifying PD-L1 More Precisely
Recent work has focused on PD-L1-associated clinical and molecular characteristics in early-stage NSCLC as perioperative immunotherapy becomes more widely used. A 2025 study investigated the prognostic value of PD-L1 in patients receiving neoadjuvant immune checkpoint inhibition plus chemotherapy. Another study derived PD-L1 QCS-PMSTC, a quantitative measure of tumor cells with medium-to-strong staining intensity, and classified patients with values of at least 0.575% as biomarker-positive.
PD-L1 Is Not the Whole Story
The phase 3 HARMONi-2 trial illustrates a limitation of treating PD-L1 status as a complete treatment guide: ivonescimab, a PD-1/VEGF bispecific antibody, significantly improved progression-free survival over pembrolizumab monotherapy in PD-L1-positive NSCLC, including the subgroup with PD-L1 of at least 50%. Separately, different PD-L1 immunohistochemistry assays have been used across NSCLC trials, with particular assays linked to different checkpoint-inhibitor treatments. These findings point to both biological limits of PD-L1 prediction and technical variation in how PD-L1 is measured.
Comparing Treatment Strategies
Comparative research has evaluated PD-1/PD-L1 inhibitors for stage III and IV NSCLC using overall survival, progression-free survival, objective response rate, disease control rate, and severe treatment-related or immune-related adverse events. For patients with PD-L1-positive advanced NSCLC without targetable genomic alterations, a 2026 report found that sacituzumab tirumotecan plus pembrolizumab significantly prolonged progression-free survival compared with pembrolizumab alone. In the PD-L1 tumor proportion score 1% to 49% group, the relative performance of immune checkpoint inhibitor plus chemotherapy versus ipilimumab plus nivolumab-based therapy had not been evaluated in the cited study.
Beyond PD-L1: The Future of Personalized Immunotherapy
While PD-L1 testing has limitations, research is actively exploring new and improved biomarkers to predict immunotherapy response. One promising avenue is tumor mutational burden (TMB), which measures the number of mutations in a tumor's DNA. Studies suggest that patients with high TMB may respond better to certain immunotherapies, regardless of their PD-L1 status.
A More Cautious Interpretation
PD-L1 testing remains clinically useful, but the available evidence suggests it should be interpreted as one part of treatment assessment rather than as a complete explanation of response. Variation in tissue sampling, assay methods, and tumor biology can make a single result difficult to generalize. A cautious approach therefore places PD-L1 within the wider clinical and molecular context.
Beyond a Single Biomarker
Reviews of current and future NSCLC immunotherapies describe continuing development beyond established PD-1/PD-L1 and CTLA-4 approaches. Future treatment selection is expected to depend on broader biomarker strategies and evolving immunotherapeutic combinations. Comprehensive testing that includes immunohistochemistry, fluorescence in situ hybridization, and next-generation sequencing is identified as critical for accurate therapeutic management.
The Limits of Standardization
The debate over PD-L1 reflects a broader challenge in precision oncology: a biomarker can be clinically important without being uniformly predictive. Differences in specimen quality, laboratory methods, interpretation, and access to comprehensive testing may affect how consistently results guide care. These limitations support a more individualized and multimodal approach, although the best combination of tests remains an evolving question.
Evidence in Everyday Care
Contemporary real-world data on advanced NSCLC treatment patterns across PD-L1 expression levels and testing status remain limited. A 2026 single-center retrospective study of patients with metastatic NSCLC and high PD-L1 expression found numerical differences in progression-free survival between first-line PD-1 and PD-L1 inhibitor monotherapy, but no statistically significant difference. Such findings underscore why treatment experiences outside clinical trials may not map neatly onto PD-L1 categories alone.
Another approach involves analyzing gene expression signatures, which reflect the activity of different genes within the tumor and its microenvironment. These signatures can provide a more comprehensive picture of the tumor's immune landscape and predict response to specific treatments.
As research progresses, the integration of multiple biomarkers – including TMB, gene signatures, and potentially refined PD-L1 assessments – will likely lead to more personalized and effective immunotherapy strategies for NSCLC. The ultimate goal is to ensure that the right patients receive the right treatment at the right time, maximizing benefit and minimizing unnecessary side effects.