The concept is deceptively simple, but the engineering is anything but. A classical ADC must remain stable in circulation, recognize its target antigen on the tumor surface, bind specifically, and then be internalized so the payload can enter the lysosome and trigger programmed cell death. Every component matters. The antibody is usually a humanized immunoglobulin G1, chosen for its long serum half-life of roughly two to three weeks and its ability to recruit immune effector mechanisms such as antibody-dependent cell-mediated cytotoxicity. The linker, whether cleavable or non-cleavable, governs when and where the toxin is released. The payload itself must be extraordinarily potent, because only about two percent of an administered ADC dose ever reaches its target antigen, demanding warheads two to six orders of magnitude stronger than standard chemotherapy drugs.

Among the payload classes, tubulin inhibitors such as auristatins and maytansines sabotage cell division, while DNA-damaging agents including topoisomerase I inhibitors, calicheamicins, and pyrrolobenzodiazepines attack the genome directly. A third emerging category uses immunomodulators such as Toll-like receptor and STING agonists to rouse innate immunity. One of the most consequential design features is the bystander effect: membrane-permeable payloads released either inside a tumor cell or in the surrounding microenvironment can diffuse into neighboring cells with low or absent antigen expression, killing tumor cells that would otherwise escape. The drug-to-antibody ratio, determined by the conjugation chemistry, is a delicate balancing act, since lowering it reduces toxicity but also weakens antitumor activity.

No target illustrates the clinical promise of ADCs better than TROP2, a transmembrane glycoprotein highly expressed in roughly 64 percent of lung adenocarcinomas and 75 percent of lung squamous cell carcinomas, where it drives proliferation, invasion, and metastasis. Datopotamab deruxtecan, a humanized anti-TROP2 antibody linked to the topoisomerase I inhibitor DXd, extended median progression-free survival to 4.4 months versus 3.7 months with docetaxel in the phase III TROPION-Lung01 trial, with the benefit concentrated in non-squamous disease, where PFS reached 5.5 months. While overall survival did not reach statistical significance in the overall population, grade three or higher treatment-related adverse events were far less frequent than with chemotherapy. In combination with pembrolizumab in TROPION-Lung02, objective response rates climbed to nearly 55 percent regardless of PD-L1 expression, and pairing the drug with the bispecific antibody rilvegostomig in TROPION-Lung04 produced a confirmed response rate of 57.5 percent with disease control in 95 percent of patients.

Chinese-developed agents are pushing the field further. Sacituzumab tirumotecan, the first domestically developed TROP2 ADC in China, carries a proprietary toxin at a high drug-to-antibody ratio of 7.4 and produced striking results in EGFR-mutant NSCLC: in the OptiTROP-Lung03 trial it nearly tripled progression-free survival compared with docetaxel, at 6.9 versus 2.8 months, with no interstitial lung disease observed. When combined with the immunotherapy tagitanlimab as first-line treatment in OptiTROP-Lung01, the confirmed response rate reached 66.7 percent, and even patients with PD-L1 scores below one percent, who typically respond poorly to immunotherapy alone, achieved a 47.1 percent response rate and 12.4 months of progression-free survival. A phase III trial is now testing this combination against standard chemo-immunotherapy in that difficult population. Sacituzumab govitecan, meanwhile, showed a clinically meaningful survival benefit in patients refractory to prior immunotherapy in the EVOKE-01 study, even though the overall result narrowly missed its statistical threshold.

HER2-targeted ADCs have delivered perhaps the most dramatic transformation. Before their arrival, patients with HER2-mutant NSCLC faced response rates below 15 percent and progression-free survival of only three to four months on standard chemotherapy. Trastuzumab deruxtecan changed that calculus entirely: in DESTINY-Lung02, the 5.4 mg/kg dose produced a confirmed response rate of 50 percent, progression-free survival of 10 months, and median overall survival of 19 months, while the Chinese DESTINY-Lung05 study confirmed a 56.9 percent response rate and 21 months of overall survival, with sustained intracranial control of brain metastases. The next-generation agent trastuzumab rezetecan, known as SHR-A1811, went further still, achieving an unprecedented 73.4 percent response rate and 11.5 months of progression-free survival in heavily pretreated patients, with an interstitial lung disease incidence of just 8.5 percent and a discontinuation rate of only 2.1 percent. The eribulin-based BB-1701 added a 50 percent response rate in a small phase II study, though efficacy in HER2-overexpressing disease remains unresolved.

The target landscape continues to widen. The c-MET-directed ADC SHR-1826 achieved a 39.7 percent response rate and 94.8 percent disease control rate among 58 evaluable NSCLC patients, offering a new strategy against a pathway notorious for driving resistance to EGFR inhibitors. The Nectin-4-targeting SHR-A2102 produced a 43.5 percent response rate in heavily pretreated EGFR-mutant patients, and the integrin beta-6-targeting sigvotatug vedotin reached a 32.5 percent response rate in taxane-naive non-squamous disease, rising to 42.9 percent when combined with pembrolizumab in the first-line setting. Most ambitious of all are bispecific constructs such as izalontamab brengitecan, which targets both EGFR and HER3 simultaneously; in pooled phase I and II analyses of EGFR-mutant NSCLC after TKI failure, it delivered a 48.8 percent response rate, 6.9 months of progression-free survival, and 24.8 months of overall survival, with interstitial lung disease occurring in fewer than one percent of patients, supporting its advance to global phase III registration.

Yet the review is candid about the field’s vulnerabilities. Resistance emerges through multiple routes: tumors downregulate or shed the target antigen, mask it with extracellular matrix proteins, upregulate efflux pumps such as MDR1 and ABCG2 that expel the payload, impair internalization through altered endocytic pathways, or raise lysosomal pH so the linker never releases its cargo. In TROP2-directed therapy, antigen-negative subclones gradually dominate under treatment pressure, while resistance to trastuzumab deruxtecan frequently involves HER2 extracellular domain truncations that preserve kinase activity but eliminate antibody binding. Toxicity remains a serious concern, above all interstitial lung disease, a potentially fatal inflammation of lung tissue associated particularly with topoisomerase I inhibitor payloads, which demands baseline pulmonary testing, vigilant imaging, and prompt corticosteroid intervention. And perhaps most frustratingly, reliable predictive biomarkers are still lacking: conventional immunohistochemistry scores correlate inconsistently with outcomes, and no standardized thresholds exist across platforms, although emerging tools such as circulating tumor DNA analysis and spatial transcriptomics offer hope for smarter patient selection.

The future directions outlined by the authors suggest the field is only beginning to mature. ADCs are moving into earlier disease settings, with the NeoCOAST-2 trial showing that perioperative datopotamab deruxtecan plus durvalumab and chemotherapy achieved a 35.2 percent pathological complete response rate in resectable NSCLC, the best among all tested cohorts. Novel targets including B7-H3, PTK7, and AXL are entering clinical evaluation, while next-generation engineering, from conditionally activated smart linkers and dual-payload constructs to site-specific conjugation platforms and PROTAC-based warheads, aims to widen the therapeutic window. Combination strategies with immune checkpoint inhibitors, EGFR tyrosine kinase inhibitors, and even radiotherapy are under active investigation. What emerges from this sweeping analysis is a clear trajectory: ADCs are transitioning from a promising salvage option to a foundational pillar of NSCLC care, and the coming decade will determine whether rational design, biomarker integration, and combination science can convert their remarkable response rates into durable, personalized cures.

Subject of Research: Antibody–drug conjugate therapy for non-small cell lung cancer

Article Title: Antibody–drug conjugates in non-small cell lung cancer: current landscape and future directions

Article References: Chen, X., Wu, S., Li, F., Yao, C., Liu, Y., & Zhou, G. (2026). Antibody–drug conjugates in non-small cell lung cancer: current landscape and future directions. Holistic Integrative Oncology, 5(1), Article 56. https://doi.org/10.1007/s44178-026-00276-7

Image Credits: AI Generated

DOI: 10.1007/s44178-026-00276-7

Keywords: antibody–drug conjugates, non-small cell lung cancer, TROP2, HER2, c-MET, datopotamab deruxtecan, sacituzumab tirumotecan, trastuzumab deruxtecan, bispecific antibodies, drug resistance, interstitial lung disease, biomarkers

The clinical stakes are enormous. Digestive system cancers are among the most common malignancies in China and worldwide, and HER2-positive subtypes account for a meaningful share of them: roughly 12 to 13 percent of gastric cancers test positive for HER2, along with about 7 percent of colorectal cancers and between 5 and 20 percent of biliary tract cancers. Two HER2-targeted ADCs, trastuzumab deruxtecan and disitamab vedotin, have already been approved by China’s National Medical Products Administration for later-line treatment of advanced HER2-positive gastric or gastroesophageal junction adenocarcinoma, while trastuzumab deruxtecan has gained approvals in more than 65 countries since its first United States authorization in December 2019. As these drugs move into routine practice across primary and secondary care settings, the experts argue, standardized safety management becomes as important as the drugs’ celebrated efficacy.

At the heart of the consensus is a clear-eyed explanation of why ADCs cause harm at all. These drugs couple a HER2-directed monoclonal antibody to a cytotoxic payload through a chemical linker, and toxicity arises from both on-target and off-target mechanisms. On-target toxicity occurs when normal cells that also express HER2 internalize the conjugate and release the payload, an unavoidable consequence of imperfect antigen specificity. Off-target toxicity follows at least four distinct routes: Fc receptor-mediated nonspecific binding by immune cells; macropinocytosis-driven uptake driven by the drug’s surface charge or hydrophobic properties; premature payload release when linkers hydrolyze in the bloodstream or are cleaved by extracellular proteases; and the so-called bystander effect, in which released payloads diffuse out of tumor cells and are taken up by neighboring healthy tissue. Understanding these pathways, the authors contend, is the foundation for rational monitoring and intervention.

Hematologic toxicity dominates the safety profile. Neutropenia, driven by the direct suppressive effect of free payload on bone marrow myeloid progenitors and by Fc-mediated immune activation, occurs in 63 percent of gastric cancer patients treated with trastuzumab deruxtecan, with more than half of those cases reaching grade 3 or worse, and febrile neutropenia arising in 4.8 percent. With disitamab vedotin, neutrophil counts fall in 50.6 percent of patients. The consensus recommends primary prophylaxis with granulocyte colony-stimulating factor for high-risk patients—those over 65, with prior chemotherapy, bone marrow involvement, liver or renal impairment, or a history of febrile neutropenia—and advises patients to check their temperature, practice rigorous hand and oral hygiene, and avoid crowds. Thrombocytopenia, linked to off-target uptake of the drugs by megakaryocytes, affects 39 percent of gastric cancer patients on trastuzumab deruxtecan and prompts strong recommendations for thrombopoietic agents when platelets fall below 50 × 10⁹ per liter, along with practical precautions such as soft toothbrushes and electric razors.

Anemia is equally pervasive, reaching incidences of 58 percent with trastuzumab deruxtecan, 49.6 percent with disitamab vedotin, and as high as 68.8 percent in biliary tract cancer, where more than half of cases are grade 3. The consensus attributes this to direct damage of erythroid progenitors and nonspecific injury to the bone marrow microenvironment, and it calls for a multidisciplinary approach combining red cell transfusion, iron supplementation, erythropoiesis-stimulating therapy, and nutritional support. Notably, the experts emphasize patient education: monitoring hemoglobin, recognizing warning signs such as resting heart rates above 100 beats per minute and exertional breathlessness, eating heme iron–rich foods paired with vitamin C while avoiding coffee and tea with supplements, and restricting vigorous activity when hemoglobin drops below 80 grams per liter.

Gastrointestinal side effects receive equally granular attention. Nausea strikes 63 percent of gastric cancer patients on trastuzumab deruxtecan and vomiting 26 percent, driven by the topoisomerase I inhibitor payload damaging GI epithelium and triggering serotonin release from enterochromaffin cells. Real-world evidence proved dual antiemetic prophylaxis insufficient for some patients, prompting the NCCN to reclassify trastuzumab deruxtecan as highly emetogenic in January 2023, though ESMO retains the moderate label. The Chinese consensus recommends prophylactic antiemetics 30 minutes before infusion, continued for two to four days afterward, using dexamethasone plus a 5-HT3 receptor antagonist for standard-risk patients and adding an NK1 antagonist for high-risk ones, with olanzapine or mirtazapine reserved for refractory cases. Diarrhea, affecting 32 percent of gastric cancer patients on trastuzumab deruxtecan, is managed by a graded scheme: oral rehydration and loperamide for mild cases, hospitalization with fluid resuscitation and octreotide for severe or complicated presentations.

The most feared toxicity is interstitial lung disease, whose mechanisms include uptake by alveolar macrophages, bystander payload release, and possibly the amino-methylene spacer in the linker itself. Incidence ranges from 3.2 percent in Chinese gastric cancer patients in the DESTINY-Gastric06 trial to 20 percent with ARX788, with median onset around 84.5 days for trastuzumab deruxtecan. Because ILD is a diagnosis of exclusion, the consensus mandates ruling out infection, metastasis, and radiation pneumonitis, classifying subtypes on chest CT—organizing pneumonia is most common at 63.1 percent, while diffuse alveolar damage carries the gravest prognosis with roughly 42 percent mortality—and recommends high-resolution chest CT every 8 to 12 weeks, serum KL-6 monitoring, and pulse oximetry at each visit. Treatment is strictly graded: brief corticosteroids and a treatment pause for grade 1 disease, permanent drug discontinuation with at least 1 milligram per kilogram daily of prednisolone for grade 2 or higher, and immunosuppressants, antifibrotics, or biologics for refractory cases.

Liver injury, neurotoxicity, and ocular toxicity round out the organ-specific guidance. Hepatotoxicity, an on-target effect demonstrated in studies of trastuzumab emtansine binding HER2 on hepatocytes, manifests as AST and ALT elevations in up to 58 percent of patients, yet the consensus explicitly advises against routine prophylactic hepatoprotective drugs, reserving close monitoring for high-risk patients such as those with viral hepatitis, who should receive antiviral therapy before starting an ADC. Peripheral neuropathy, driven by free monomethyl auristatin E disrupting the neuronal microtubule network, affects nearly a third of patients on disitamab vedotin and is managed with B vitamins, neuroprotective agents, and gabapentinoids. Ocular toxicity is essentially confined to ARX788, which caused dry eye in 63.3 percent of treated patients, prompting recommendations for baseline eye screening and prompt ophthalmology referral. The document also flags the uncertain but potentially synergistic pulmonary risk when ADCs are combined with immune checkpoint inhibitors.

Dosing philosophy and team structure complete the framework. The consensus endorses 6.4 milligrams per kilogram every three weeks as the standard starting dose of trastuzumab deruxtecan in HER2-positive gastric cancer, based on superior efficacy over 5.4 milligrams per kilogram in phase I expansion and confirmation in DESTINY-Gastric01 and 06, with stepwise reductions to 5.4 and then 4.4 milligrams per kilogram and no re-escalation once reduced; disitamab vedotin starts at 2.5 milligrams per kilogram every two weeks, reducible to 2.0 or 1.5. Complex or severe adverse events should be routed through a structured multidisciplinary team led by an oncologist and including pulmonology, hepatology, ophthalmology, neurology, radiology, and clinical pharmacy. Perhaps most distinctively, the guideline champions a physician-led, patient-engaged model of education, arguing that informed patients who recognize early symptoms of infection, bleeding, breathlessness, or numbness are the first line of defense—experience the authors believe will transfer directly to the next generation of ADCs targeting other oncogenic pathways.

Subject of Research: Safety management of adverse events from HER2-targeted antibody–drug conjugates in digestive system cancers

Article Title: Chinese expert consensus on the management of adverse events to HER2-targeted antibody–drug conjugates in digestive system cancers (2025 edition)

Article References: Yu, Y., Wu, J., Lv, M., Cui, Y., Dai, G., Deng, T., Gong, L., Li, J., Li, H., Lin, R., Liu, Y., Peng, Z., Rao, S., Wang, F., Wang, F., Wei, J., Wu, S., Xue, J., Yang, W., … Liu, T. (2026). Chinese expert consensus on the management of adverse events to HER2-targeted antibody–drug conjugates in digestive system cancers (2025 edition). Clinical Cancer Bulletin, 5(1), Article 1. https://doi.org/10.1007/s44272-025-00053-z

Image Credits: AI Generated

DOI: 10.1007/s44272-025-00053-z

Keywords: HER2, antibody-drug conjugates, trastuzumab deruxtecan, disitamab vedotin, gastric cancer, biliary tract cancer, interstitial lung disease, adverse event management, expert consensus, drug safety, oncology, multidisciplinary team

Fibrotic interstitial lung diseases comprise a diverse group of disorders that progressively destroy the delicate tissue of the lung parenchyma. Idiopathic pulmonary fibrosis, the archetypal member of this family, is almost always progressive, characterized by worsening breathlessness, a steady loss of lung capacity, and ultimately respiratory failure and death. Other interstitial lung diseases, including those driven by autoimmune conditions, hypersensitivity reactions, or occupational exposures, may also evolve into a progressive fibrotic phenotype, now termed progressive pulmonary fibrosis, which shares much of the grim natural history of idiopathic pulmonary fibrosis. Before the arrival of antifibrotic drugs, therapeutic options were limited, and median survival after diagnosis was measured in just a few years.

Weight loss and malnutrition have long been recognized as poor prognostic markers in chronic lung disease. In chronic obstructive pulmonary disease, for example, dietary supplementation in malnourished patients has been shown to improve exercise capacity, respiratory function, and health-related quality of life. The role of nutrition in idiopathic pulmonary fibrosis and progressive pulmonary fibrosis has been far less well understood, in part because body weight in these patients can be influenced by many competing forces. Reduced exercise tolerance and corticosteroid use may push weight upward, while disease symptoms and medication side effects can suppress appetite and drive unintended loss. Studies vary widely in reported malnutrition prevalence, but a consistent finding has emerged across cohorts: unintentional weight loss is associated with worse outcomes.

The evidence is striking. Japanese and United Kingdom cohort studies in idiopathic pulmonary fibrosis demonstrated that an annual body weight loss of 6.1 percent predicted lower survival, even in patients in whom a decline in forced vital capacity, the standard measure of lung function, was not observed. A Danish survey of one hundred patients found that those reporting unintentional weight loss of at least five percent of body weight at baseline faced significantly higher risks of mortality and hospital admission within a year. In a multicentre study, both body mass index and weight loss were independently associated with one-year mortality in fibrotic interstitial lung disease. A meta-analysis of thirty-four studies encompassing more than eighteen thousand patients confirmed that low baseline body mass index and weight loss during the disease course were independent predictors of mortality.

To explore these relationships in the context of modern therapy, the review authors examined data from the pivotal Phase III trials of nintedanib. The INPULSIS program randomized 1,066 patients with idiopathic pulmonary fibrosis to nintedanib 150 mg twice daily or placebo, reporting annual rates of forced vital capacity decline of minus 239.9 milliliters and minus 207.3 milliliters in the placebo arms, which improved to minus 114.7 and minus 113.6 milliliters respectively with treatment. A pooled analysis demonstrated an overall reduction in the annual rate of decline of 109.9 milliliters with nintedanib. The INBUILD trial similarly randomized 663 patients with progressive fibrosing interstitial lung disease to the same treatment regimen. Crucially, both trials collected detailed data on baseline body mass index and weight change over fifty-two weeks, allowing investigators to stratify outcomes by nutritional status.

The findings from the placebo arms paint a consistent picture. Patients with lower body mass index, below 25 kilograms per square meter, experienced numerically greater annual decline in forced vital capacity than those in the mid-range of 25 to under 30 or the obese range of 30 and above. Likewise, patients who lost more than five percent of their body weight over the trial year declined faster than those who lost less or gained weight. Adverse associations extended to other endpoints as well, with lower baseline body mass index and unintended weight loss both linked to poorer outcomes overall. The new and previously unpublished analyses of pooled INPULSIS data added an important refinement: the deleterious effect of weight loss on lung function was most pronounced in patients who started with a body mass index below 25, was still evident in those in the overweight range who lost more than five percent of body weight, and was not observed at all in patients with obesity.

The relationship between weight loss, lung decline, and mortality proved complex rather than linear. In the INPULSIS placebo arm, patients losing more than five percent of body weight had numerically fewer deaths than those with lesser weight change, a finding the authors caution was based on exploratory analyses with limited events and was not powered for mortality comparisons. In INBUILD, by contrast, a four-kilogram weight decrease corresponded to an increased risk of acute exacerbation or death in multivariable analysis, though not to a greater risk of disease progression. These discordances likely reflect the multifactorial nature of mortality in fibrotic lung disease, differences in baseline characteristics between populations, and the fact that forced vital capacity decline and death capture related but distinct dimensions of disease severity.

A central question hovered over the entire analysis: because nintedanib itself commonly causes gastrointestinal side effects, including diarrhoea, nausea, and appetite loss, could treatment-induced weight loss undermine the drug’s benefits? The data emphatically answer no. Weight loss exceeding five percent over fifty-two weeks occurred in 37.8 percent of nintedanib-treated patients in INPULSIS compared with 20.1 percent on placebo, and in 55 percent of nintedanib patients in INBUILD versus 39 percent on placebo. Yet in the nintedanib arms, the rate of forced vital capacity decline was similar between patients with and without significant weight loss, at roughly 103 versus 121 milliliters per year, and the treatment effect versus placebo was preserved across every body mass index subgroup. Indeed, the greatest benefit was observed in patients with lower body mass index and those experiencing weight loss, suggesting the antifibrotic effect operates independently of nutritional status.

The review also situates these findings within a broader body composition literature that moves beyond simple scales. Body mass index cannot distinguish fat mass from lean mass, and recent work indicates that lung function in fibrotic disease correlates with muscle quantity and quality, with sarcopenia associated with poor prognosis. Fat-free mass index has been significantly correlated with survival in idiopathic pulmonary fibrosis, the Geriatric Nutritional Risk Index predicts both prognosis and antifibrotic continuation rates, and bioimpedance-derived phase angle outperformed traditional measures in discriminating patients with worse lung function and quality of life. Measures of skeletal muscle attenuation have been associated with lung function and functional capacity, underscoring that not all weight loss carries the same physiological meaning.

The authors conclude that nutritional advice and weight monitoring should form an integral component of supportive care, with targeted strategies aimed at patients at highest risk, particularly those with low baseline body mass index who subsequently lose weight. Practical recommendations include increasing protein intake, eating smaller and more frequent meals to counteract appetite loss, and maintaining hydration to manage gastrointestinal toxicities, while adherence to a Mediterranean diet has been associated with improved lung function in related populations. A recent pilot randomized controlled trial demonstrated that specialist dietary intervention is feasible in patients experiencing unintentional weight loss, though definitive evidence that nutrition directly modifies long-term outcomes remains limited. Most importantly, the findings reinforce a message for patients and clinicians alike: rather than discontinuing antifibrotic therapy when gastrointestinal effects and weight loss emerge, every effort should be made to manage these side effects and maintain adherence, because the preservation of lung function that these drugs deliver outweighs the metabolic cost, and the antifibrotic shield holds firm regardless of what the scale says.

Subject of Research: The impact of weight loss and body mass index on outcomes in nintedanib clinical trials for interstitial lung disease.

Article Title: Review of the Impact of Weight Loss and Body Mass Index in Clinical Trials of Nintedanib in Interstitial Lung Disease

Article References: Kreuter, M., Kottmann, R. M., Luo, F., Coeck, C., Kanakapura, M., Schlecker, C., Ritter, I., & Handa, T. (2026). Review of the Impact of Weight Loss and Body Mass Index in Clinical Trials of Nintedanib in Interstitial Lung Disease. Advances in Therapy. https://doi.org/10.1007/s12325-026-03785-z

Image Credits: AI Generated

DOI: 10.1007/s12325-026-03785-z

Keywords: nintedanib, idiopathic pulmonary fibrosis, progressive pulmonary fibrosis, weight loss, body mass index, interstitial lung disease, forced vital capacity, antifibrotic therapy, malnutrition, nutrition, INPULSIS, INBUILD

Ulcerative colitis is well known for the symptoms it causes in the large intestine, but it belongs to a family of conditions whose influence is systemic. Extraintestinal manifestations affect up to 27 percent of patients, and among these, lung disease has been increasingly appreciated. One large cohort study of 563 patients with ulcerative colitis identified lung involvement in 5 percent, with organising pneumonia accounting for 1.8 percent. Yet that same study attributed nine of the ten organising pneumonia cases to drug-induced mechanisms, leaving open a fundamental question: can organising pneumonia arise as a primary, disease-intrinsic feature of ulcerative colitis itself, independent of any medication?

The new case suggests that it can. The 2025 update to the international multidisciplinary classification of the interstitial pneumonias, issued jointly by the European Respiratory Society and the American Thoracic Society, now explicitly lists ulcerative colitis among the secondary causes of cicatricial organising pneumonia, a histologically distinct entity. That formal recognition matters, because it provides a framework for attributing lung disease to the underlying bowel condition rather than defaulting to a drug reaction—a distinction with direct consequences for how patients are treated.

The patient at the centre of the report was a lifelong never-smoker with a ten-year history of ulcerative colitis pancolitis, maintained on a stable dose of mesalamine at 2.4 grams daily. She carried a concurrent diagnosis of rheumatoid arthritis, made five years after her colitis began, based on bilateral symmetric polyarthritis affecting fifteen small joints with finger nodules. Two biologic drugs, adalimumab and certolizumab, had been trialled and discontinued for lack of efficacy. Three months before admission, her pulmonary function tests had been entirely normal. Then she developed progressive shortness of breath over the course of a single month.

On admission, she required low-flow oxygen, and examination revealed crackles in both lungs. Crucially, a faecal calprotectin measurement obtained one month earlier stood at 62 micrograms per gram, below the 80 micrograms per gram threshold that identifies histological bowel activity—a biomarker-confirmed remission. Her systemic inflammatory markers, however, told a different story: C-reactive protein, erythrocyte sedimentation rate and white cell count were all elevated. High-resolution computed tomography of the chest showed bilateral interstitial haziness, predominantly in the mid and lower lung fields, representing clear progression from prior imaging that had shown only mild scattered scarring.

Diagnostic workup proceeded along two tracks. Bronchoalveolar lavage fluid revealed a differential cell count of 42 percent neutrophils and only 3 percent lymphocytes—a profile that would later prove important. A transbronchial cryobiopsy of the right lower lobe was performed, and the initial histopathological interpretation locally was fibrotic non-specific interstitial pneumonia, a diagnosis that prompted plans for antifibrotic therapy with mycophenolate and nintedanib. But when the slides were reviewed by expert pulmonary pathologists, the interpretation changed fundamentally. The expert consultation identified organising pneumonia, characterised by polypoid fibroblast plugs known as Masson bodies within the airspaces, with only mild background fibrosis and an absence of honeycomb change or fibroblast foci—the hallmarks that would have supported a diagnosis of usual interstitial pneumonia or fibrotic non-specific interstitial pneumonia.

That diagnostic reversal was directly consequential. The planned antifibrotic regimen was abandoned in favour of corticosteroid therapy, the standard treatment for organising pneumonia, which carries a five-year survival exceeding 90 percent when treated appropriately. The patient received three days of intravenous pulse methylprednisolone followed by oral prednisone with a planned six-month taper. Mesalamine was held as a precaution, but withholding the drug produced no clinical improvement on its own—further evidence against a drug-induced mechanism. Follow-up imaging at two months showed partial resolution of the bilateral infiltrates, with residual changes consistent with her pre-existing baseline scarring, and azathioprine was added as a steroid-sparing agent with the additional benefit of maintaining her colitis.

The authors lay out a careful argument for why this organising pneumonia was disease-intrinsic rather than drug-induced. First, mesalamine exposure had been stable for a decade; drug-induced pneumonitis typically appears within weeks to months of initiation or dose change. Second, discontinuation of the drug during hospitalisation brought no improvement, whereas corticosteroids were required for a response—inconsistent with the natural history of a drug reaction. Third, the 2025 classification now formally recognises ulcerative colitis as a secondary cause of cicatricial organising pneumonia. The case also extends the sole prior published report of organising pneumonia occurring after histologically confirmed ulcerative colitis remission, adding biomarker-confirmed remission, systematic drug exclusion, detailed lavage data and a complete autoimmune workup that reclassified the patient’s joint disease as ulcerative colitis-associated spondyloarthropathy rather than rheumatoid arthritis, removing rheumatoid-associated lung disease from the differential.

Perhaps the most scientifically intriguing observation is the lavage profile. Classic cryptogenic organising pneumonia typically shows lymphocytic predominance in bronchoalveolar lavage, with lymphocyte counts of 20 to 40 percent and only mild neutrophil elevation. This patient showed the reverse: 42 percent neutrophils and a mere 3 percent lymphocytes. Prior research has shown that secondary organising pneumonia carries lower lymphocyte counts than the cryptogenic form, and the authors hypothesise that ulcerative colitis-associated disease may carry a distinctly neutrophil-predominant signature reflecting immune cell trafficking along the gut-lung axis. Mouse studies lend plausibility to this idea: colitis has been shown to induce pulmonary neutrophil infiltration through interleukin-17 elevation and microbial translocation, and interleukin-6-driven, neutrophil-mediated pulmonary inflammation has been documented in murine models of colitis with bacteremia.

The case is also a cautionary tale about diagnostic uncertainty in interstitial lung disease. The discordance between the local reading of fibrotic non-specific interstitial pneumonia and the expert reading of organising pneumonia mirrors a documented pitfall of cryobiopsy interpretation: intraluminal Masson bodies within airspaces favour organising pneumonia, whereas interstitial fibroblast foci within the alveolar wall characterise the fibrotic pneumonias. The CAN-ICE trial found only fair between-center agreement for cryobiopsy-based diagnoses, with a kappa of 0.29. In this instance, expert pathology review changed the entire treatment trajectory, and the authors argue that such review should be considered routine whenever cryobiopsy-based diagnoses drive major therapeutic decisions. Two cases over thirteen years may reflect genuine rarity, the authors concede, but under-recognition is equally plausible, given that prior cohorts attributed drug causation without systematic exclusion criteria. For clinicians, the message is twofold: organising pneumonia can flare during biomarker-confirmed bowel remission, and drug-induced causes must be rigorously excluded before the lung disease is attributed to the bowel condition—because the correct diagnosis determines whether a patient receives antifibrotics or steroids, a fork in the road with very different prognoses.

Subject of Research: A case of disease-intrinsic organising pneumonia occurring during biomarker-confirmed ulcerative colitis remission

Article Title: Disease‐Intrinsic Organising Pneumonia During Biomarker‐Confirmed Ulcerative Colitis Remission

Article References: Disease‐Intrinsic Organising Pneumonia During Biomarker‐Confirmed Ulcerative Colitis Remission. (n.d.). https://doi.org/10.1002/rcr2.70702

Image Credits: AI Generated

DOI: 10.1002/rcr2.70702

Keywords: ulcerative colitis, organising pneumonia, extraintestinal manifestations, gut-lung axis, cryobiopsy, interstitial lung disease, bronchoalveolar lavage, corticosteroids, ERS/ATS classification, mesalamine, inflammatory bowel disease, Masson bodies

COPA syndrome is caused by mutations in the COPA gene, which encodes the alpha subunit of the coatomer protein complex, a cellular machine responsible for shuttling proteins between the endoplasmic reticulum and the Golgi apparatus. When this trafficking system breaks down, proteins accumulate abnormally within cells, triggering cellular stress and activating the type I interferon pathway, a central alarm system of innate immunity. The result is profound immune dysregulation characterized by the production of autoantibodies and chronic inflammation that primarily targets the lungs, kidneys and joints. The condition is usually inherited in an autosomal dominant pattern, although sporadic cases without any family history occur, and the classic clinical triad comprises interstitial lung disease or diffuse alveolar hemorrhage, arthritis and kidney disease.

The patient at the center of the report first fell ill at the age of 27, when he developed flu-like symptoms, coughing up blood and acute respiratory failure severe enough to require orotracheal intubation and eighteen days of mechanical ventilation. Chest computed tomography at that time revealed diffuse alveolar damage and a nonspecific interstitial pneumonia pattern. Within the same year he began showing signs of renal dysfunction, and a year later he suffered a second episode of acute respiratory failure. Given the striking combination of lung bleeding and kidney injury, his physicians initially suspected a pulmonary–renal syndrome such as ANCA-associated vasculitis or Goodpasture syndrome, and in 2008 he was started on an intensive course of twelve cycles of the immunosuppressant cyclophosphamide.

That treatment achieved partial stabilization, but it could not halt the underlying disease. Serial chest CT scans over the following years documented progressive fibrotic damage to the lungs, including upper lobe–predominant honeycombing, increasing reticulation, traction bronchiectasis and persistent ground-glass opacities. By 2022, high-resolution imaging showed established fibrotic remodeling alongside findings suggesting active inflammatory lung injury, a coexistence of chronic scarring and recurrent acute damage that is characteristic of the heterogeneous pulmonary manifestations of COPA syndrome. A transbronchial biopsy yielded inadequate tissue, so the surgical team proceeded to an open lung biopsy. The histopathology proved remarkably rich: prominent lymphoid follicles consistent with follicular bronchiolitis, a non-fibrotic nonspecific interstitial pneumonia pattern with marked interstitial edema, patches of organizing pneumonia containing intra-alveolar fibrin in an acute fibrinous and organizing pneumonia pattern, fibrin thrombi within airspaces, and evidence of both recent and remote alveolar hemorrhage in the form of hemosiderin-laden macrophages.

The kidneys told a parallel story. A renal biopsy performed in November 2008 demonstrated focal proliferative and necrotizing glomerulonephritis with early crescent formation in six of nine glomeruli examined, confirming active immune-mediated renal injury. Immunofluorescence showed no linear deposition of immunoglobulin along the glomerular basement membrane, which definitively excluded Goodpasture syndrome. Serologic testing during reevaluation between 2021 and 2022 revealed a positive antinuclear antibody test at a titer of 1:320 in a homogeneous pattern and a positive p-ANCA at 1:80, but antibodies directed against myeloperoxidase, proteinase 3, double-stranded DNA, Smith, ribonucleoprotein, Ro/SSA and La/SSB were all negative. Kidney function was impaired, with a creatinine clearance of 60 mL per minute and 24-hour proteinuria of 907.5 mg. The atypical ANCA positivity, the authors note, reflects the immune dysregulation inherent to COPA syndrome rather than primary ANCA-associated vasculitis, a distinction with major consequences for classification and treatment.

The definitive answer arrived only in January 2024, when next-generation sequencing identified a heterozygous COPA variant, NM_004371.4:c.698G>A (p.Arg233His), classified as likely pathogenic under American College of Medical Genetics criteria. This variant had been reported previously in individuals with COPA syndrome and is associated with pulmonary and autoimmune manifestations, and its identification finally unified the patient’s pulmonary hemorrhage, crescentic glomerulonephritis and arthralgia under a single genetic diagnosis. Notably, the patient had denied any family history of autoimmune, interstitial lung or renal disease, and genetic testing of relatives was unavailable, underscoring how sporadic presentations can escape suspicion for years. Pulmonary function testing in 2022 revealed a mixed moderate obstructive and restrictive ventilatory defect, with a forced vital capacity of 53 percent predicted, a forced expiratory volume in one second of 44 percent predicted and a markedly reduced diffusing capacity for carbon monoxide at 42 percent predicted. A six-minute walk test showed oxygen saturation falling from 96 percent to 85 percent after only 285 meters.

Once the diagnosis was confirmed, the nephrology team initiated maintenance immunosuppression with methotrexate 10 mg weekly and prednisone 10 mg daily, and the patient remained clinically stable and asymptomatic for roughly a year. The course then deteriorated for reasons that were tragically behavioral as much as biological. The patient self-adjusted his medications, discontinued methotrexate without medical advice because he attributed his symptoms to a viral infection, and stopped attending scheduled follow-up visits. After approximately a year without immunosuppressive therapy, he returned with worsening renal function and significant proteinuria while his lung disease remained stable. Suspecting immune-mediated renal relapse, clinicians began pulse cyclophosphamide at 1 g daily for three consecutive days together with pulse methylprednisolone at the same dose and schedule, with no documented neutropenia during treatment.

Shortly after that single cycle, the patient developed acute diverticulitis complicated by sepsis from a perforated diverticulum, an event for which he had no prior history of diverticular disease. He underwent an emergency Hartmann’s procedure with end colostomy for surgical source control, but despite emergency abdominal surgery and prolonged broad-spectrum antibiotics, he progressed to septic shock and multiorgan failure and died. The case authors emphasize that severe infection during potent immunosuppression is among the principal causes of mortality reported in COPA syndrome, alongside progressive respiratory failure and end-stage kidney disease, and that patients receiving cyclophosphamide and similar agents require particularly vigilant multidisciplinary monitoring.

Beyond its clinical drama, the report carries broader lessons for the field. Because COPA syndrome is rare and phenotypically variable, diagnostic delay is common, especially when adult presentations overlap with far more prevalent autoimmune and interstitial lung diseases. The authors argue that the diagnosis should be suspected in patients with diffuse alveolar hemorrhage, unexplained pulmonary–renal syndromes, follicular bronchiolitis or interstitial lung disease beginning in childhood or early adulthood, particularly when autoantibodies are positive without a definitive connective tissue disease diagnosis. Genetic testing, they contend, should be pursued whenever diagnostic uncertainty persists despite multidisciplinary evaluation. On the therapeutic horizon, Janus kinase inhibitors such as baricitinib and ruxolitinib, which target the type I interferon pathway at the root of the disease, have shown promise in case reports and small studies and may prove especially valuable for severe or refractory disease. The authors call for multicenter studies and international registries to standardize treatment strategies and define the natural history of the condition, and they conclude that early recognition, sustained treatment adherence and careful monitoring during immunosuppressive therapy are essential to prevent relapse and fatal complications in this rare but devastating disorder.

Subject of Research: COPA syndrome, a rare autosomal dominant genetic autoimmune disorder affecting the lungs, kidneys and joints

Article Title: A Rare Case of COPA Syndrome: Multisystem Relapse and Fatal Septic Complication

Article References: Castro Velasco Fernandes, F., Torres, P. P. T. E. S., de Paula Silveira‐Lacerda, E., Rabahi, M., Velasco Magalhaes Fernandes, L., Lopes, L. R., Moreira, M. A. R., & Rabahi, M. F. (2026). A Rare Case of COPA Syndrome: Multisystem Relapse and Fatal Septic Complication. Respirology Case Reports, 14(9), Article e70742. https://doi.org/10.1002/rcr2.70742

Image Credits: AI Generated

DOI: 10.1002/rcr2.70742

Keywords: COPA syndrome, genetic autoimmune disease, interstitial lung disease, diffuse alveolar hemorrhage, glomerulonephritis, COPA gene mutation, immunosuppression, sepsis, next-generation sequencing, type I interferon, follicular bronchiolitis, pulmonary-renal syndrome

The patient arrived at the hospital with a low-grade fever and a facial rash, one week after close contact with his daughter, who had been suffering from upper respiratory symptoms. Two years earlier he had been diagnosed with interstitial lung disease, suspected to be bird-related chronic hypersensitivity pneumonitis, a form of inflammatory lung injury driven by exposure to avian antigens such as those from feather duvets and down jackets. His condition had been managed with systemic corticosteroids, which had been carefully tapered and discontinued several months before admission, and he had been rigorously counseled to avoid avian exposures. A former smoker with a 38 pack-year history, he initially received oral levofloxacin from his local physician without improvement, prompting referral to the authors’ hospital.

On admission the clinical picture was deceptively subtle. He was alert, his temperature was 37.0 degrees Celsius, and his oxygen saturation sat at 90 percent on room air while fine crackles could be heard bilaterally and a mild facial rash was visible. Laboratory evaluation showed only mild inflammation, with a C-reactive protein level of 0.89 mg/dL, and importantly, serum KL-6 and surfactant protein D, biomarkers commonly used to track interstitial lung disease activity, remained unchanged from his baseline values. An extensive infectious workup was entirely negative, including serum beta-D-glucan, cytomegalovirus antigenemia, Aspergillus IgG and a multiplex polymerase chain reaction panel for common respiratory pathogens. Given the recent sick contact in the family and the facial rash, clinicians performed parvovirus B19 serology, which returned positive IgM and IgG antibodies, indicating a recent primary infection.

Imaging told a more alarming story. Chest radiography revealed decreased radiolucency in the bilateral middle and lower lung fields compared with films obtained only three months earlier, and high-resolution computed tomography demonstrated newly developed bilateral ground-glass opacities, a finding that in a patient with underlying fibrotic lung disease immediately raises concern for an acute exacerbation. Broad-spectrum antibiotics were started on the assumption of bacterial pneumonia, yet the opacities continued to progress, forcing the team to look deeper. Bronchoscopy was performed, and bronchoalveolar lavage fluid collected from the left B5 segment yielded a total cell count of 1.42 x 10^5 cells per milliliter with striking lymphocytic predominance of 63.5 percent, along with histiocytes at 33.8 percent, neutrophils at 1.0 percent and eosinophils at 1.7 percent.

The decisive result came from molecular testing of that lavage fluid: polymerase chain reaction was positive for parvovirus B19 DNA, directly demonstrating the virus within the lower respiratory tract during the acute phase of illness. Testing for Pneumocystis jirovecii was negative, no pathogenic organisms were isolated in culture, and cytology excluded malignancy. With a compatible exposure history, serologic confirmation of acute infection and viral DNA recovered from the lung itself, the clinicians concluded that the acute respiratory deterioration was associated with parvovirus B19, a diagnosis essentially never made in immunocompetent adults. During hospitalization the serum KL-6 and SP-D levels rose and the patient’s oxygen requirement climbed transiently to 3 liters per minute, reflecting genuine physiologic worsening rather than an incidental imaging finding.

Treatment took the form of high-dose pulsed corticosteroids, with methylprednisolone at 1000 mg per day, which produced rapid clinical and radiological improvement. The patient was transitioned to tapering oral prednisolone and discharged on Day 19 of his admission. At four-month follow-up he remained clinically stable, with sustained resolution of the opacities on serial chest radiographs. The favorable response is notable, though as the authors caution, it does not by itself settle the underlying mechanism, since the suspected bird-related hypersensitivity pneumonitis is generally considered more steroid-responsive than progressive fibrotic diseases such as idiopathic pulmonary fibrosis.

The diagnostic reasoning in this case illuminates a genuine clinical dilemma. Acute exacerbation of interstitial lung disease is defined by rapid respiratory deterioration within one month and the appearance of new bilateral ground-glass opacities on high-resolution computed tomography, criteria that this patient met. Yet distinguishing primary viral pneumonia from infection-triggered acute exacerbation remains notoriously difficult because the two entities overlap substantially in their clinical and radiological features. Previous prospective work cited by the authors detected respiratory viral infections in 19.2 percent of acute exacerbation cases, and such infections are associated with poor short-term outcomes. In this instance, common culprits such as influenza virus and the herpesviruses were excluded, and the absence of any alternative infectious agent or cardiac failure strengthened the case for parvovirus B19 as the causative trigger, although the authors acknowledge that unrecognized avian antigen exposure and progression of the underlying hypersensitivity pneumonitis could not be completely excluded, particularly given the lymphocytic, rather than neutrophilic, lavage profile.

The mechanistic plausibility of parvovirus B19 lung injury rests on well-characterized virology. The virus is a small, non-enveloped, single-stranded DNA virus that enters cells by binding the P antigen, a globoside receptor expressed not only on erythroid progenitors but also on pulmonary endothelial cells. Viral interaction with this receptor may cause endothelial injury, increased vascular permeability and diffuse alveolar damage, the histological substrate of acute lung injury. Experimental studies add a pro-fibrotic dimension: the viral non-structural protein NS1 has been shown to exacerbate fibrotic processes through activation of the TGF-beta/Smad signaling pathway, while the VP1-unique region of the capsid induces inflammatory cytokine release and disrupts epithelial barriers. In a lung already scarred by chronic interstitial disease, these processes could act as a ‘second hit’ that tips a compensated patient into acute exacerbation, providing a coherent biological explanation for what the radiographs and lavage findings captured.

The authors, Tomoki Kishaba and Satoshi Marumo of the Department of Respirology at Kitano Hospital, conclude that although the relative contributions of direct viral lung injury, infection-triggered exacerbation and progression of the underlying bird-related hypersensitivity pneumonitis could not be definitively disentangled, the case highlights the importance of considering parvovirus B19 as a potential contributor to acute respiratory deterioration, particularly in patients with underlying interstitial lung disease. For clinicians, the practical lessons are concrete: a facial rash or known ‘slapped cheek’ contact in an deteriorating ILD patient should prompt parvovirus B19 serology, and bronchoalveolar lavage with viral PCR can identify pathogens that routine respiratory panels miss, since parvovirus B19 does not appear on standard multiplex panels. For virologists and pulmonologists alike, the report underscores how much remains unknown about a virus that infects roughly half of humanity by adulthood, and the authors call for further studies to clarify the mechanisms underlying parvovirus B19-associated pulmonary involvement before such life-threatening presentations are encountered again.

Subject of Research: Acute respiratory deterioration associated with parvovirus B19 infection in a patient with interstitial lung disease.

Article Title: Acute Respiratory Deterioration Following Parvovirus B19 Infection in a Patient With Interstitial Lung Disease: A Case Report

Article References: Kishaba, T., Marumo, S., Nishida, Y., Nohara, E., Higashi, J., Aoki, S., Okura, C., Jinno, S., Tashima, N., Morimoto, C., Kitajima, T., & Inoue, D. (2026). Acute Respiratory Deterioration Following Parvovirus B19 Infection in a Patient With Interstitial Lung Disease: A Case Report. Respirology Case Reports, 14(9), Article e70751. https://doi.org/10.1002/rcr2.70751

Image Credits: AI Generated

DOI: 10.1002/rcr2.70751

Keywords: parvovirus B19, interstitial lung disease, acute exacerbation, hypersensitivity pneumonitis, viral pneumonia, bronchoalveolar lavage, ground-glass opacities, corticosteroids, respiratory infection, lung fibrosis, Acute, Respiratory