A Quiet Player in Lung Cancer: Rediscovering Tumor-Draining Lymph Nodes
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For decades, lymph nodes — the foundation of lung cancer staging — were evaluated primarily to answer a single question: “Is there metastasis here or not?” If positive, the disease is at a more advanced stage, the prognosis is worse, and the treatment approach changes. However, evidence accumulated in recent years shows that tumor-draining lymph nodes (TDLN) are not simple “channels of metastasis,” but dynamic immune organs that shape the immune response against the tumor. Frontiers in Immunologypublished this comprehensive review in April 2026, showing how tumor-draining lymph nodes are being repositioned in non-small cell lung cancer (NSCLC) as both an important biomarker and a potential treatment target. This new understanding opens a broad spectrum of applications, from predicting immunotherapy response to administering treatment directly to lymph nodes accessed by EBUS.
Lymph Node Anatomy: Headquarters of the Immune System
Lymph nodes are structures that act as the immune system's “headquarters.” Three main compartments can be distinguished from the outside inward:
LYMPH NODE MICROARCHITECTURE
Cortex (outer layer) contains lymphoid follicles; it is where B cells concentrate and antibody-producing germinal centers form. Paracortex (T-cell zone) functions as the heart of cellular immunity; it is where antigen presentation and T-cell activation take place. Here, through specialized blood vessels called HEV (high endothelial venules) , CCR7+ lymphocytes gain access to the blood. Medulla (inner region) is where macrophages and plasma cells concentrate and lymph flow leaves the node. Tumor-draining lymph nodes are the main transit points through which cancer cells pass via the lymphatic route — the immune system's first major encounter with the tumor occurs here.
What we have learned from studies outside lung cancer (particularly melanoma and breast cancer) shows that these structures undergo a dramatic biological transformation. Even before tumor cells reach the lymph node, cytokines, exosomes, and growth factors secreted by the tumor turn it into a “pre-metastatic niche” — the tumor prepares favorable soil in advance.
Functional architecture of the cortex, paracortex, and medulla, and tumor-derived suppressive signals
How the Tumor Manipulates the Lymph Node: A Hidden War
Lung tumors manipulate lymph nodes through multiple mechanisms. Biologically active molecules released by tumor cells and surrounding stromal cells — growth factors, cytokines, chemokines, exosomes — systematically remodel the lymph node microenvironment. This process encompasses the following main dimensions:
- TGF-β ↑ — increases 30-fold in the draining lymph node
- IL-10 ↑ — correlates with tumor stage
- IL-12 ↓ — inversely correlates with survival
- TNF-α ↓ — the inflammatory response weakens
- VEGF-A, sVEGFR-1, Ang-2 ↑ (Saeed and colleagues)
- IL-6, uPA, sHER-2/neu, PLGF ↑
- Treg (regulatory T cells) ↑ — particularly in adenocarcinoma
- Effector CD4+ T cells ↓
- Dendritic cell maturation ↓
- CD80/86 costimulatory molecules ↓ (in mAPCs)
- PD-1+ T cells ↑ (may be a biomarker of immunotherapy response)
- Anergic (exhausted) CD4 T cells increase
The practical meaning of these changes is that even before the tumor spreads to the lymph node, the node may already have been transformed into a microenvironment that “helps the tumor.” These changes are particularly pronounced in patients with adenocarcinoma — Treg accumulation is greater than in squamous cell carcinoma, and natural killer cells decrease. This may partly explain why some immunotherapies are less effective in lung adenocarcinoma.
Micrometastasis and Stages of Metastasis: An Invisible Threat
In NSCLC, lymph node involvement — the N stage — is a cornerstone of prognosis and treatment decisions. Historically, the pathologist examined a lymph node under the microscope to determine “whether tumor cells are present.” Modern immunohistochemistry and molecular methods, however, have revealed three different degrees of involvement:
🟢 ISOLATED TUMOR CELLS (ITC)
Single cells or clusters smaller than 0,2 mm. Their prognostic value is debated; some studies show an adverse effect, while others do not.
🟡 MICROMETASTASIS (NMM)
Tumor deposits between 0,2 mm and 2 mm. Associated with reduced disease-free and overall survival — a finding that should no longer be ignored.
🔴 MACROMETASTASIS
Structured metastasis larger than 2 mm. Shows marked dysregulation of epithelial–mesenchymal transition (EMT) molecules compared with micrometastasis.
Modern bronchoscopy (EBUS-TBNA) radically changed this picture. Endobronchial ultrasound-guided transbronchial needle aspirationhas made mediastinal lymph node assessment in lung cancer minimally invasive and highly accurate. EBUS has made lymph nodes accessible not only for staging, but also for future biomarker discovery and even treatment delivery.
EBUS-TBNA: From a Staging Tool to a Research Platform
EBUS-TBNA is a cornerstone of current lung cancer practice. It allows samples to be obtained from mediastinal lymph nodes through a minimally invasive approach. This review, however, highlights that its future role could be much broader:
Metabolic Reprogramming: From Tryptophan to Asparagine
One of the most exciting aspects of tumor-draining lymph nodes investigated in recent years is metabolic reprogramming. Cancer cells and immune cells compete for the same nutrients; this competition determines which side will “win.” Several important metabolic pathways stand out:
The enzyme indoleamine-2,3-dioxygenase 1 (IDO1) converts tryptophan into kynurenine. In tumor-draining lymph nodes, IDO1+ plasmacytoid dendritic cells:
- Directly activate Tregs
- Upregulate PD-L1
- Convert naive T cells into Tregs
- Reduce T-cell effector function
Zhang and colleagues (2025) presented an important finding: lung cancer cells with high asparagine synthetase (ASNS):
- Increase their immunogenicity by autocrine secretion of α-aminobutyric acid
- Increase MHC class I expression
- In a cohort of 25 patients, high ASNS correlated with the efficacy of neoadjuvant immunotherapy
- A new candidate response biomarker
These metabolic findings open important avenues for drug development. OATD-02 and other dual arginase inhibitors may reverse immune suppression by reducing intratumoral L-arginine consumption; preclinical studies have shown increased response to immune checkpoint blockade. The link between glutamine metabolism and PD-L1 expression also offers new targets.
The Hidden Key to Immunotherapy Response: Why Do Some Patients Respond?
PD-1/PD-L1 inhibitors have revolutionized NSCLC, but the vast majority of patients do not achieve a long-term response. One of this review's most important clinical insights is: The critical spark that initiates the immunotherapy response often arises not in the tumor itself, but in the draining lymph node.
Several important lines of evidence support this: in the study by Borm and colleagues, patients who progressed after immune checkpoint inhibitor treatment had a higher frequency of Tregs in their TDLNs than responders. Yang and colleagues showed that neoadjuvant immunotherapy reduced FDG activity in the tumor bed but did not reduce activity in TDLNs — the lymph node's condition, more than control of the tumor, can predict treatment response. Tumor-involved TDLNs were associated with a poor pathological response and predicted rapid recurrence after treatment.
Radiotherapy and the Lymph Node: Should It Be Spared?
One of this review's most practical clinical messages concerns radiotherapy's effects on TDLNs. Traditional lung cancer radiotherapy fields were broad, typically including hilar and mediastinal lymph nodes in irradiation. New preclinical data and clinical studies, however, show that: Irradiating TDLNs may weaken the antitumor immune response.
The mechanism can be summarized as follows: the TDLN is where T cells are trained against the tumor and immune memory forms. Irradiating these centers may suppress the treatment-induced “abscopal effect” (regression of distant lesions). The study by Telarovic and colleagues in 2024 in Nature Communications showed that delayed adjuvant TDLN irradiation preserved the efficacy of combined radio-immunotherapy.
🟢 SPARING APPROACHES
In the study by Khalifa and colleagues, patients receiving lymph-node-sparing (LN-sparing) neoadjuvant chemoradiotherapy showed upregulated antitumor immune-response pathways (immune response, hypoxia, angiogenesis, EMT) in their TDLNs compared with controls.
🟡 THE INCREASE STUDY
Ulas and colleagues (2025): in patients with T3-4N0-2 NSCLC receiving neoadjuvant immunotherapy + chemoradiotherapy, even irradiated TDLNs showed increased CD8 and Tregs and an increased type I immune response — demonstrating that the immune response could be preserved even in the presence of radiation-induced fibrosis.
The Effect of Surgery: VAMLA and Systemic Immune Improvement
A series of studies that may be particularly interesting for Türkiye concerns the systemic immune improvement observed after video-assisted mediastinoscopic lymphadenectomy (VAMLA). These studies, to which Turkish research teams also contributed (Engin and colleagues, 2023; Cikman and colleagues, 2023), showed:
✅ IMPROVEMENT IN T-CELL FUNCTION
After VAMLA, PD-1 and CTLA-4 expression decreased in peripheral-blood cytotoxic T cells — the T cells lost their signs of “exhaustion.” Granzyme A expression also increased — T cells regained active cytotoxic function.
✅ STRENGTHENING OF NATURAL KILLER CELLS
Cikman and colleagues: the proportion of effective NK cells increased, the exhausted NK subgroup decreased, and cytotoxic activity (LAMP-1, granzyme A) improved. Lymph node removal thus “set free” the body's cancer-fighting NK cells.
These findings suggest that the positive effect of lymph node dissection on survival in NSCLC may involve not only “removing metastatic nodules,” but also reducing systemic immune suppression — a meaningful update to the philosophy of surgical oncology.
The Tumor-Draining Lymph Node: A Drug Target of the Future
Perhaps the most exciting aspect of this review is the potential to use the tumor-draining lymph node as a direct drug target . Compared with systemic treatment, this approach permits delivery of a high concentration of the active agent with far fewer side effects. Clinical trials currently under way:
CAN-2409: Adenovirus-based viral immunotherapy + immune checkpoint inhibitor combination, with intratumoral/intralymph-node administration in stage III/IV NSCLC.
JNJ-87704916: Intratumoral administration of a multi-armed oncolytic virus — monotherapy and combination treatment in solid tumors.
NBTXR3 (hafnium nanoparticles): A radiosensitizer administered with reirradiation in inoperable locoregionally recurrent NSCLC.
These approaches rest on the following rationale: treatments administered directly to lymph nodes — for example, mRNA vaccines delivered by lipid nanoparticles, dendritic cell vaccines, or small-molecule immunomodulators — concentrate at the target site before reaching the systemic circulation and directly trigger antitumor immunity. Direct drug administration to tumor-draining lymph nodes under EBUS guidance could represent a future paradigm shift.
Previously discussed on drozdogan.com, otojen sevumeran (BioNTech-Genentech) and other personalized mRNA vaccines for pancreatic cancer have shown success, and MATISSE (anti-CD39, IPH5201) and other adenosine-pathway inhibitors have produced lung cancer phase 2 results that provide strong evidence that lymph-node-targeted approaches will shape oncology's future.
Critical Appraisal: Limitations and Open Questions
Although this review paints an exciting picture, critical appraisal is essential. Several important limitations and open questions remain:
🔴 SMALL SAMPLES AND SINGLE-CENTER STUDIES
The vast majority of existing studies are based on small samples (10-50 patients). Multicenter, randomized validation studies remain limited. The findings need to be replicated in large populations.
🔴 NO SINGLE BIOMARKER
There is not yet a TDLN biomarker that can predict treatment response “on its own.” Multiple-marker panels are promising, but are not ready for clinical use.
🟡 TECHNICAL CHALLENGES
EBUS-TBNA samples are limited in quantity; obtaining enough material for single-cell RNA sequencing and extensive immunophenotyping is technically difficult. Standard protocols have not yet been established.
🟡 INTERTUMORAL HETEROGENEITY
Differences in PD-L1 expression and driver mutations between the primary tumor and metastatic lymph node have been demonstrated; this complicates treatment selection and clinical trial design.
🟡 THE GENERAL STAGING SYSTEM
The clinical significance of isolated tumor cells (ITC) is debated; the current TNM staging system does not account for micrometastasis and immune profiles. Discussions of updates to the AJCC system continue.
Implications for Practice in Türkiye
This review has several important strategic messages for NSCLC practice in Türkiye. First, Turkish researchers' active role in this field is noteworthy — the studies by Engin, Cikman, Turna, and Esen's team showing immune improvement after VAMLA are a concrete example of Türkiye's contribution to international literature. Extending this kind of research infrastructure to other major thoracic surgery centers could strengthen Türkiye's position in pulmonary oncology research.
Second, EBUS-TBNA is becoming increasingly widespread in Türkiye — it is routinely performed in major university and private hospitals. However, EBUS samples are not systematically stored in biobanks and used for translational research . A national EBUS sample biobank established through cooperation between TÜBİTAK and major oncology centers (Memorial, Acıbadem, MD Anderson, university hospitals) would be an important infrastructure investment enabling Turkish scientists to contribute to international lymph node research.
Third, assessing TDLNs as biomarkers of immunotherapy response could create additional economic value within Türkiye's SGK system — early identification of patients who will not respond would allow millions of liras to be used effectively. Fourth, standardizing lymph-node-sparing (LN-sparing) radiotherapy planning in Türkiye's radiation oncology centers has the potential to improve immunotherapy efficacy. Finally, evaluating direct immunotherapy administration to lymph nodes (intranodal mRNA, dendritic cell vaccines) in clinical research in Türkiye is important for our patients' early access to innovative treatments.
🎓 DROZDOGAN Academy — Commentary and Discussion
TUMOR-DRAINING LYMPH NODE · IMMUNE MICROENVIRONMENT · BIOMARKER · NSCLC · IMMUNOTHERAPY TARGETING
The Importance of This Review
In oncology practice, the lymph node was used for decades as a “staging tool”; a positive finding meant a poor prognosis, while a negative finding meant a good one. This conceptual framework strongly guided clinical practice — but modern immunology is making its inadequacy increasingly clear. The tumor-draining lymph node is not merely a passive channel of metastasis; it is the first major meeting point between tumor and immune system, a critical headquarters where antitumor immunity forms — or is suppressed. This review comprehensively presents the rapidly expanding evidence base for this new understanding in lung cancer. The message for oncology practitioners is clear: we should no longer ask only “How many are positive in the pathology report?”; we should also consider what is happening inside that lymph node, which cytokines are being produced, which T cells predominate, and how they shape treatment response. In the EBUS-TBNA era, this information is becoming increasingly accessible.
Strengths
The methodological strength of Bain and colleagues' review lies in its multilayered perspective: anatomy, the cytokine microenvironment, cellular composition, genomic and transcriptomic changes, metabolic reprogramming, and clinical applications are considered together. The role of modern technologies (single-cell RNA sequencing, high-parameter flow cytometry, multi-omic analyses) in lymph node research is clearly emphasized. Table 1 synthesizes the research landscape of the last 20 years, providing a chronological map of the field's development — a valuable reference for young researchers learning about the area. Practical clinical applications, such as predicting immunotherapy response, radiotherapy planning, and the effects of surgery, are explicitly discussed. The study also emerges from a specialized research infrastructure such as the NYU Pulmonary Oncology Research Team (NYU PORT), reflecting the leadership of groups that use EBUS-TBNA as a research platform. The inclusion of studies by Turkish researchers (the Engin, Cikman, and Turna team) in this international review is an important indicator of local scientists' contribution to international literature.
Limitations and Open Questions
Critical appraisal highlights the following points. First, the review's main limitation is the limitations of the studies it synthesizes — many are small, single-center, observational studies. The claim that “the TDLN immune profile determines treatment response” may therefore overinterpret the current evidence base; what is involved is correlation rather than causation. Second, generalizing data from melanoma and breast cancer to lung cancer is problematic — NSCLC has distinctive tumor-microenvironment features, and these differences have sometimes been overlooked. Third, the review falls short in providing concrete, actionable recommendations for clinical practice — after stating that “the TDLN immune profile is important,” it does not develop specific guideline recommendations such as “perform this test in this patient group and make this decision.” Fourth, economic reality has been neglected — TDLN immune profiling is costly, and its feasibility in low- and middle-income health systems is debatable. Fifth, while an excessively hopeful tone is used for treatments administered directly to TDLNs (intranodal mRNA vaccines, dendritic cell vaccines), uncertainties about their long-term safety, immunogenicity, and cost are insufficiently emphasized. Sixth, the review reflects the NYU PORT research group's perspective, and certain interests (ongoing clinical trials) may have influenced the observer's impartiality. Finally, the role of AI-assisted imaging and data analysis in TDLN assessment is insufficiently explored — developments in this area are rapid, and it will be a central topic for future reviews.
Implications for Clinical Practice
The concrete messages that can be drawn from this review for thoracic oncology practice in Türkiye are as follows. First, samples obtained during EBUS-TBNA for NSCLC staging should increasingly be stored not only for pathological diagnosis, but also for molecular and immune analysis . This should become standard practice. This lays the foundation for future translational research. Second, in patients with NSCLC for whom immunotherapy is planned, it should be remembered that tumor PD-L1 expression alone is insufficient and that TDLN expression may also shape decisions in the future — for now this remains a research area, but it may influence clinical decisions in the near future. Third, radiation oncology planning teams should consider that wide-field radiotherapy routinely targeting TDLNs may suppress antitumor immunity ; lymph-node-sparing approaches should be considered, particularly in patients scheduled for concurrent or sequential immunotherapy. Fourth, the positive effect on survival of surgical procedures such as mediastinoscopic lymph node dissection (VAMLA) may involve not only “removing metastatic nodules,” but also reducing systemic immune suppression — a reality demonstrated by Turkish researchers; this is an important point that surgical oncology teams can emphasize when speaking with patients. Fifth, it is strategically important for major pulmonology and oncology centers in Türkiye to prepare to participate in future trials of TDLN-targeted treatments (intranodal vaccines, local immunomodulators). Finally, when communicating that a patient has a “positive lymph node,” framing it not merely as “bad news,” but as “a biological reality that provides information about the interaction between the tumor and the immune system” may strengthen the patient's engagement with the oncological narrative.
Future Questions
The critical questions for the coming period are these: when will response biomarkers based on the TDLN immune profile (Treg/CD8 ratio, cytokine signatures, IDO1 expression, etc.) be validated as a panel suitable for clinical use? Can single-cell RNA sequencing and high-parameter flow cytometry of EBUS-TBNA samples become standard laboratory techniques, and can their cost be reasonable? Will direct administration of immunomodulators to TDLNs (intranodal mRNA, oncolytic virus, dendritic cell vaccine) demonstrate efficacy in clinical phase 2/3 studies in patients who do not respond to immunotherapy? When will lymph-node-sparing radiotherapy approaches (LN-sparing CRT) be integrated into standard NSCLC protocols, and will clinical benefit be shown? Can differences in the TDLN immune profile between adenocarcinoma and squamous cell carcinoma guide histology-specific treatment selection? Can Turkish researchers' studies of VAMLA and its systemic immune effects be validated in multicenter, prospective cohorts, and can a survival benefit be proven? Can AI-based multi-omic data analysis standardize the clinical assessment of TDLNs? Could a national EBUS biobank and translational research platform be established in Türkiye through cooperation between TÜBİTAK, universities, and the private sector? Finally, how should the ethical framework of research tests such as TDLN immune profiling be shaped within the process of informed consent with patients? These questions will shape the next 10 years of NSCLC treatment and the outcomes of millions of patients with lung cancer.
Scientific References
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This article was created using various editorial tools, including artificial intelligence, as part of the process. It was reviewed by human editors before publication.
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