This Week in Pulmonary — May 21, 2026

Welcome to This Week in Pulmonary. This week we're covering 8 notable papers spanning pulmonary vascular disease, the tumor microenvironment in lung cancer, and new insights into airway diseases like asthma and IPF. Let's dive in.

Advances in Pulmonary Arterial Hypertension We begin in pulmonary arterial hypertension, with two studies that provide new perspectives on its structural and molecular basis.

First, in The European Respiratory Journal, a study used micro-computed tomography to create detailed 3D maps of the pulmonary vasculature in explanted lungs from patients with end-stage PAH [1].

The Study Investigators compared lungs from seven patients with idiopathic or heritable PAH to five healthy controls. They performed a quantitative analysis of arterial lumen diameter, the number of small acinar vessels, and the distribution of plexiform lesions.

Results Compared to controls, the PAH lungs showed a 50% reduction in the diameter of the acinar arterial lumen and a 61% decrease in the number of intra-acinar arterioles. This provides objective, quantitative evidence of the vascular pruning that characterizes the disease. The degree of arterial narrowing correlated directly with hemodynamic measures like pulmonary vascular resistance and mean pulmonary artery pressure. The study also found that patients with heritable PAH had a higher number of plexiform lesions, which were located more distally within the acinus, compared to those with idiopathic PAH. This finding may help explain the more severe phenotype often seen in heritable disease.

Conclusions The paper concludes that this vascular rarefaction may be an initiating process in PAH, rather than just a secondary phenomenon. This work solidifies the structural underpinnings of increased PVR in PAH.

While that study focused on structure, a second paper in Science Translational Medicine investigated the molecular mechanism of sotatercept, a promising new therapy for PAH [8]. It's been thought that sotatercept works by rebalancing BMP and TGF-beta signaling, particularly by boosting the deficient BMPR-II pathway. This study challenges that simple model.

The Study Researchers developed and validated a peripheral blood transcriptomic biomarker panel to measure BMP pathway activity, overcoming the challenge of inaccessible lung tissue. They then used this panel in a pilot study of nine PAH patients treated with sotatercept to measure target engagement.

Results Surprisingly, the analysis suggested that sotatercept did not rebalance or increase BMPR-II pathway signaling. Instead, it led to a reduction in signaling. The authors propose this might be due to the drug acting as a ligand trap, depleting circulating BMP9 and BMP10. The study also found that specific transcriptomic signatures in the blood were associated with clinical outcomes and mortality, highlighting the potential of these biomarkers.

Discussion Together, these two papers paint a fuller picture of PAH. The micro-CT study [1] gives us a stark, quantitative look at the vascular destruction at the heart of the disease. The sotatercept study [8] reminds us that even when a therapy works, its mechanism of action may be more complex than initially thought, and that robust biomarkers are critical for understanding target engagement in clinical trials.

The Immune Microenvironment in Lung Disease Next, we turn to the complex interplay between the immune system and lung pathology, with new findings in both lung cancer and idiopathic pulmonary fibrosis.

A fascinating paper in Cell uncovers a neuroimmune axis that promotes lung cancer progression [7]. It's known that sensory nerves regulate lung physiology, but their role in cancer has been unclear.

The Study Using mouse models of lung adenocarcinoma, researchers investigated the interaction between sensory nerves, immune cells, and tumor growth. They found that lung tumors locally amplify nociceptive, or pain-sensing, sensory nerve innervation.

Results This increased nerve activation leads to the release of the neuropeptide CGRP. CGRP then acts on a subset of macrophages, which in turn impairs the recruitment of specific fibroblasts responsible for building tertiary lymphoid structures, or TLS. These structures are critical for organizing an effective anti-tumor immune response, and their presence is a key predictor of better prognosis. By blocking TLS formation, the nerve-CGRP axis effectively suppresses T cell and B cell-dependent immunity, allowing the tumor to grow. The researchers showed that local sensory denervation or pharmacologic blockade of CGRP restored TLS formation and suppressed tumor growth. Importantly, exposure to cigarette smoke extract activated this same neural circuit, accelerating cancer progression independent of its mutagenic effects. In these animals, blocking CGRP sensitized tumors to immunotherapy and prolonged survival.

Discussion This study identifies a novel mechanism by which smoking promotes lung cancer and reveals how tumors co-opt the nervous system to create an immunosuppressive microenvironment. This CGRP pathway represents a potential new therapeutic target.

Providing broader context for this type of immune dysregulation, a review in Thorax explores the role of lymphocytes in idiopathic pulmonary fibrosis [6]. While IPF is defined by fibrosis, there is growing evidence that immune dysregulation is a pivotal part of its pathogenesis. The review summarizes the current knowledge on how both conventional immune cells, like CD4 and CD8 T cells, and unconventional T cell subsets contribute to fibrosis. These unconventional cells, such as natural killer T cells, are known for their rapid, antigen-independent activation and their role in tissue repair. The article suggests their interactions with fibroblasts and epithelial cells could position them as key modulators of lung injury and fibrosis, making them potential targets for future immunomodulatory therapies in IPF.

Clinical Practice Updates in Diagnosis and Staging Our third theme focuses on papers with direct implications for clinical practice, including major new guidelines for lung cancer staging and a new perspective on asthma exacerbations.

Published in The European Respiratory Journal, we have new clinical practice guidelines on the use of endobronchial and esophageal endosonography for the diagnosis and staging of lung cancer [3]. These were developed jointly by the European Respiratory Society, the European Society of Gastrointestinal Endoscopy, and the European Society of Thoracic Surgeons.

Recommendations For clinicians who perform or refer for these procedures, the recommendations are clear. First, for mediastinal nodal staging in non-small cell lung cancer, endosonography is recommended over surgical mediastinoscopy as the initial test. Second, the guidelines suggest systematic staging of all reachable nodes is the minimal standard, rather than just targeting nodes that appear abnormal on imaging. Third, they state that combined EBUS and EUS, ideally performed in a single session, is preferred over EBUS alone for the most comprehensive evaluation. Fourth, after a negative endosonography result, add-on mediastinoscopy is not recommended as a routine step. Endosonography is also suggested for restaging after induction therapy. For tissue acquisition, standard 21 or 22-gauge needles are considered the standard of care, with insufficient evidence to support routine use of other needle types or cryobiopsy. Finally, the guidelines confirm that EBUS-TBNA provides samples with a high suitability rate for PD-L1 assessment.

Also in The European Respiratory Journal, a multicenter observational study provides a potential mechanistic link between obesity and severe asthma exacerbations [2].

The Study Investigators studied 1,169 adults with asthma, performing clinical characterization, spirometry, and impulse oscillometry, or IOS, to assess small airway dysfunction, known as SAD. They then looked for associations between BMI, SAD, and severe exacerbations.

Results They found that SAD, as defined by IOS, was significantly more common in individuals with a BMI of 30 or greater. The risk of having SAD roughly doubled for obese patients compared to non-obese patients. This relationship was non-linear, with lung function parameters deteriorating more steeply once BMI exceeded a threshold of about 28 to 30. Furthermore, SAD itself was independently associated with a near doubling of the odds of having a severe exacerbation in the past year. A mediation analysis estimated that this small airway dysfunction accounted for 26 to 41 percent of the total association between obesity and exacerbation risk. Standard spirometry provided little additional information.

Conclusions This study positions small airway dysfunction as a key functional trait underlying poor outcomes in obese asthma patients, and suggests it could be a specific 'treatable trait' to target in this population.

Foundations of Research: From Metabolism to Methods Finally, we'll briefly touch on two papers that reinforce the foundations of our clinical evidence, one exploring fundamental metabolic signaling and the other refining how we should interpret clinical trials.

A paper in Nature challenges the conventional view of a metabolite called L-2-hydroxyglutarate, or L-2-HG [5]. In humans, a deficiency of the enzyme that clears this metabolite leads to a severe neurologic disease, and so L-2-HG has long been considered simply toxic. This work suggests it also has a crucial physiological function. The researchers demonstrated that its levels are actively regulated within mitochondria and that it acts as a signaling molecule to repress the transcription of specific genes by modifying histones. In mouse models, systemically reducing L-2-HG levels by overexpressing its clearing enzyme led to impaired postnatal growth, kidney problems, and early mortality. This work establishes L-2-HG as a physiological signaling metabolite and serves as a powerful reminder that molecules we label as 'toxic' may have complex and essential biological roles.

And in the BMJ, a consensus statement provides a much-needed extension to a framework for defining research questions in clinical trials [4]. The original framework, called ICH E9(R1), introduced the concept of the 'estimand' to force researchers to be precise about what treatment effect they are actually trying to estimate. However, it was focused on individually randomized trials. This new paper extends the framework to cluster randomized trials, where groups of people, like patients in different clinics, are randomized together. These trials present unique challenges for interpretation. The new CRT-Estimands Framework provides a clear set of attributes that should be described when defining the research question in a cluster trial. Adopting this framework will improve the clarity of these trials, helping clinicians and policymakers make better-informed decisions based on their results.

If you only have time for one paper this week, make it the ERS/ESGE/ESTS clinical practice guidelines on endosonography for lung cancer, published in the European Respiratory Journal [3]. These comprehensive recommendations will directly shape the diagnostic and staging pathways for lung cancer in centers across Europe and beyond, reinforcing the central role of endosonography.

Here are the key takeaways from this week in Pulmonary.

First: In lung cancer, new European guidelines firmly place endosonography as the initial procedure of choice for mediastinal staging, recommending a systematic approach and combined EBUS/EUS over mediastinoscopy.

Second: In obese patients with asthma, consider small airway dysfunction as a key, potentially treatable, mechanism driving exacerbations. Impulse oscillometry can help identify this trait.

Third: Our understanding of PAH pathophysiology continues to evolve. Micro-CT imaging confirms that vascular pruning is a central quantitative feature, while new biomarker data suggests the mechanism of sotatercept may be more complex than simple rebalancing of the BMP pathway.

Finally: The tumor microenvironment is a key battleground. A new study in Cell identifies a neuro-immune axis where sensory nerves suppress anti-tumor immunity by blocking the formation of tertiary lymphoid structures, offering a novel target for therapy, particularly in smokers.

That's your roundup for This Week in Pulmonary. The full transcript and references are available on the episode page in your AudioScholar library. This is an AI-curated summary — for clinical decisions, always consult primary sources and current guidelines. See you next week.

This is an automated summary generated by artificial intelligence, which can make mistakes. Always review the original source materials.