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Abstract Background Idiopathic pulmonary fibrosis (IPF) is a chronic progressive fibrosing interstitial lung disease that continues to have high morbidity and mortality. There are only 3 approved medications, (nintedanib, pirfenidone and nerandomilast) which marginally slow FVC decline and only nerandomilast having some mortality benefit. All three have no effect on quality of life (exacerbations and hospitalizations). There is an urgent need to find more effective treatment options. Since IPF is predominantly a disease of the elderly with a peak prevalence in those 65 and older, it is common for these individuals to have other comorbidities such as Hyperlipidemia (HLD). Interestingly, in a prior small study of IPF patients, there is evidence to suggest clinical benefit from ezetimibe, a medication used to treat HLD. This study aims to further evaluate the clinical benefits of ezetimibe in patients with IPF in a large national cohort. Methods We conducted this study using the Optum Labs Data Warehouse (OLDW). The OLDW contains de-identified administrative claims data, including medical and pharmacy claims and enrollment records. This study used claims data from commercial, Medicare Advantage (MA), and Medicare Fee-for-service (FFS) enrollees between October 1st, 2014, and December 31st, 2021. Diagnosis of IPF was defined using ICD-9 and ICD-10 codes. Patients without a diagnosis of IPF were excluded. P < 0.05 was set to determine statistical significance. Two matched patient cohorts depending on ezetimibe use were defined. Primary outcome was all-cause mortality, and secondary outcome was hospitalizations. Results We identified 7724 patients with IPF. After adjusting for age, age group, gender, race, health plan, year of IPF diagnosis, smoking, diabetes, statin treatment, and antifibrotic treatment, two cohorts were identified and matched, patients treated with ezetimibe (n = 3862) and patients not treated with ezetimibe (n = 3862). Among the patients with IPF treated with ezetimibe, ezetimibe use was associated with a reduction in all-cause mortality (hazard ratio [95% CI]: 0.704 [0.660 - 0.752], p-value: <0.001) and hospitalizations(hazard ratio [95% CI]: 0.907 [0.857 - 0.959], p-value: 0.001) compared to patients not treated with ezetimibe. Conclusion In patients with IPF, treatment with ezetimibe may be associated with improved clinical outcomes. Further studies are necessary to confirm benefits, assess anti-fibrotic effects, and inform implementation in management of IPF. As IPF remains a disease with limited treatment options, repurposing drugs continues to offer an avenue to find affordable, safe and already approved medications for use. This abstract is funded by: None

Abstract Rationale Interstitial lung abnormalities (ILA) are abnormal findings on chest CT scans that may represent early-stages of interstitial lung disease. The presence of fibrosis (traction bronchiectasis and/or honeycombing) identifies those with ILA at an increased risk for mortality, however, determining who will progress remains a challenge, and the role of blood-based biomarkers in ILA risk-stratification is unknown. Methods Data from four prospective cohort studies were used to identify associations between plasma proteins measured with DNA aptamers (SomaScan) and ILA, fibrosis, and mortality. The Genetic Epidemiology of COPD Study (COPDGene) was used to identify protein associations, and findings were replicated by meta-analysis of the Age, Gene/Environment Susceptibility-Reykjavik study (AGES-Reykjavik), SubPopulations and InteRmediate Outcome Measures in COPD Study (SPIROMICS), and Framingham Heart Study (FHS). Protein associations with ILA and with fibrotic ILA compared to non-fibrotic ILA were performed using multivariable logistic regression; among those with ILA, Cox proportional hazards models were used to identify protein associations with mortality. Models were adjusted for age, gender, race, BMI, smoking status, pack-year smoking history, and for mortality, COPD. Benjamini-Hochberg false discovery rate p-values <0.05 were considered significant. Results 524 (10.7%) of 4,899 COPDGene participants had ILA, of whom 57 (10.9%) had fibrosis; of 8,146 AGES-Reykjavik, SPIROMICS and FHS participants included in the meta-analysis, 666 (8.2%) had ILA, of whom 198 (29.7%) had fibrosis. In COPDGene, 230 proteins were associated with ILA; the most significant of which were SFTPD (adjusted odds ratio per standard deviation [SD] of protein [OR]=2.21, p = 3.7E-41) and SFTPB (OR = 1.82, p = 7.9E-37). In the meta-analysis, 159 of the ILA-associated proteins were replicated. Of the 230 ILA-associated proteins in COPDGene, 9 were associated with fibrosis, and 5 of these 9 proteins were associated with mortality among those with ILA. The 5 proteins associated with all three outcomes were WFDC2 (ORILA=1.90, p = 2.6E-34; ORFibrosis=2.00, p = 0.0001; adjusted hazards of mortality per SD of protein [HR]=1.59, p = 3.4E-05), GDF15 (ORILA=1.67, p = 3.6E-23; ORFibrosis=1.78, p = 0.0006; HR = 1.63, p = 1.4E-06), SCGB3A1 (ORILA=1.52, p = 4.5e-14; ORFibrosis=1.80, p = 0.0002; HR = 1.25, p = 0.02), TREM1 (ORILA=1.44, p = 1.4e-14; ORFibrosis=1.62, p = 0.001; HR = 1.25, p = 0.02) ICAM5 (ORILA=1.42, p = 1.2e-11; ORFibrosis=1.79, p = 0.0001; HR = 1.31, p = 0.002). In the meta-analysis, 6 of the 9 fibrosis-associated proteins and all 5 ILA mortality-associated proteins replicated. Conclusion This represents the first plasma proteomic screen demonstrating reproducible biomarker associations not only with ILA presence, but also with measures of severity and adverse outcomes. These results provide compelling targets for further study, including their prospective evaluation as clinical biomarkers for early disease identification and prognostication. This abstract is funded by: Multiple Sources

Abstract Introduction Burkholderia, Achromobacter, and Stenotrophomonas species are associated with worse clinical outcomes in cystic fibrosis (CF),1 though little is known about their prevalence or pathogenicity in non-CF bronchiectasis (pwBE). Herein we describe the prevalence and clinical characteristics of pwBE who isolated each of these three organisms. Methods We conducted a retrospective cross-sectional analysis of baseline data from the US Bronchiectasis and Nontuberculous Mycobacteria (NTM) Research Registry (BRR). Adult bronchiectasis patients with known Achromobacter, Burkholderia cepacia complex (BCC), or Stenotrphomonas maltophilia culture results were included. Patients were stratified according to the presence of at least one positive culture among the gram-negative species. Demographics, clinical characteristics, and first annual follow-up culture results were summarized descriptively for the overall study population and between groups. No inferential analyses or hypothesis testing was performed. Results 5003 pwBE met the inclusion criteria, of which 39 (0.78%) isolated Achromobacter species, 11 isolated Burkholderia (0.22%), and 288 isolated Stenotrophomonas maltophilia (5.8%). Patients with Achromobacter were older, with a median age (interquartile range) of 76 (73.0-79.0) years, compared to the overall bronchiectasis cohort (69.0 years). Those with Burkholderia or Stenotrophomonas were younger, at 69.0 (53.0-75.0) and 71.0 (63.0-77.0) years, respectively. A high proportion of those with Achromobacter were male (31%) versus those with Burkholderia (9%) and Stenotrophomonas (24%), were current or former smokers (46%), were more likely to have had one or more exacerbations in the 2 years prior to enrollment (87%) than the overall BE cohort (57%), and were more likely to have had pulmonary-related hospitalization than those with either Burkholderia or Stenotrophomonas (46% vs. 27% and 19%, respectively). PwBE who isolated Burkholderia were less likely to have co-colonization with Pseudomonas aeruginosa or NTM species (9% each). At first annual follow-up, no patients with baseline Burkholderia isolated them at follow-up, and only 31% with baseline Stenotrophomonas isolated it at follow-up. Conclusion Overall prevalence of Achromobacter, Burkholderia, and Stenotrophomonas species in the BE cohort was low. Patients who isolated Achromobacter species were older, more likely to be current or former smokers, and more likely to experience pulmonary exacerbation and hospitalization. 15 patients who had not previously isolated Achromobacter, and 3 patients who had not previously isolated Burkholderia did so at annual follow-up. Interestingly, no patients with baseline Burkholderia isolates went on to isolate it at annual follow-up, which contradicts earlier studies in pwCF.2 The number of patients isolating Burkholderia in the U.S. BRR is very low, thereby limiting interpretation. This abstract is funded by: None

Abstract Background Prostaglandin E2 (PGE2) exerts paradoxical effects in asthma, acting as both a protective mediator and a contributor to pathology depending on context. Its role is shaped by type 2 (T2)-status, eosinophilia, and exacerbation frequency. In epithelial cell cultures from asthmatic and healthy individuals, interleukin (IL)-13 suppresses PGE2 synthesis genes (PTGS2 and PGES) while upregulating HPGD, which encodes for the PGE2 catabolic enzyme 15-prostaglandin dehydrogenase (15-PGDH) (PMID:16751012), suggesting diminished PGE2 availability during T2 inflammation. Similarly, in aspirin-exacerbated respiratory disease (AERD), impaired cyclooxygenase disrupts PGE2 biosynthesis, fueling unchecked leukotriene production and eosinophilic inflammation (PMID: 30516547), underscoring PGE2’s protective role in limiting disease progression. Conversely, in nasal polyps, tuft cells are activated by IL-13 to produce PGE2 (PMID: 35608904), highlighting PGE2’s potential pathogenicity. Objective To assess associations between PGE2-pathway gene expression in bronchial brushings and asthma severity, and to determine how nasal polyp history modifies these relationships. Methods We analyzed bronchial epithelial brushings from 109 adults with asthma (mean age 42.4±12.1, 64% female, 52% severe asthma, 18% nasal polyps) using normalized and batch-corrected RNA-seq data from the baseline visit in the Severe Asthma Research Program (SARP)3 (PMID: 36796454). Age-adjusted and nasal polyp-adjusted relationships were calculated between ratios of PGE2 synthesis and metabolism genes and clinical outcomes (ASSESS score, FEV1 %predicted). The composite PGE2 score (PMID: 35608904), derived from nasal polyp analysis, was calculated from the average scaled log-normalized expression of six PGE2-responsive genes. All data were analyzed using a linear regression mixed model with a random effect for site. Results Ratios of PGE2 synthesis genes (PTGS1/2, PTGES2) to HPGD were significantly associated with greater disease severity (change in ASSESS Score) (Fig.1A, solid lines) and lower lung function (change in FEV1 %predicted) (Fig.1B, solid lines). These relationships persisted after adjusting for nasal polyps (Fig.1, dashed lines). The composite PGE2 score was also related to disease severity (Fig.1A, black solid line) but attenuated when nasal polyps were accounted for (Fig.1A, black dashed lines). Interestingly, lower lung function remained associated with the PGE2 score even after nasal polyp adjustment (Fig.1B, dashed black lines). Conclusions Our analysis demonstrates that the balance between PGE2 synthesis and degradation in the bronchial epithelium is closely linked to asthma severity and lung function, independent of nasal polyp status. Future work will integrate transcriptomic and clinical data longitudinally to establish whether PGE2 could serve as a biomarker for asthma trajectory. This abstract is funded by: HL115118 (LCD), U10HL109152 (S.E.W.), U10HL109172 (to E.I. and B.D.L), U10HL109168 (N.N.J.), U10HL109250 (S.C.E), U10HL109164 (W.C.M), U10HL109257 (M.C), and U10HL109146 (to P.G.W. and S.A.C.)

Abstract Rationale Type-1 inflammation in asthma leads to significant airway level changes independent of Type-2 inflammation and may underlie the severity seen in combined Type1/2 high disease. As IFNs can cause airway epithelial injury and impaired repair, we applied a novel interpretable machine learning algorithm, SLIDE, to analyze the transcriptome of airway epithelial brushings of mild-moderate (MMA) and severe asthma (SA) participants in the Immune Mechanisms in Severe Asthma (IMSA) cohort to identify latent/hidden factors of disease that associate with disease severity. Methods The expression of genes identified by SLIDE as part of a co-expression program was assessed in the full IMSA cohort by severity and in an independent cohort of the NHLBI Severe Asthma Research Program (SARP). We also examined associations of these genes with clinical asthma outcomes in both cohorts. Results SLIDE identified aberrant increased expression of membrane-tethered mucin genes, MUC1 and MUC4. MUC1 appeared in each of 5 significant latent factors associated with greater severity and MUC4 in 2/5. Standard DGE analysis also identified the gene CEACAM5 as a predictor of severity. Pathway analysis of latent factor genes revealed airway keratinization which may contribute to airway remodeling and worsening obstruction over time. Expression of MUC1, MUC4, and CEACAM5 were increased in SA compared to HC in both the full IMSA and separate SARP cohorts (p < 0.001 for all genes in both cohorts). Expression in MMA was consistently lower than in SA in both cohorts, reaching significance in IMSA (p < 0.01) but not consistently in SARP (MUC1 p = 0.04, MUC4 p = 0.27, CEACAM5 p = 0.27). Protein analysis of endobronchial biopsies by immunofluorescence staining showed a trend towards increased MUC1 protein content with evidence of secretion. MUC1, MUC4 and CEACAM5 were negatively correlated with FEV1 % predicted in both cohorts (IMSA: MUC1 r=-0.47, p < 0.01, MUC4 r=-0.47, p < 0.01, CEACAM5 r=-0.62, p < 0.01; SARP: MUC1 r=-0.19, p = 0.05, MUC4 r=-0.29, p < 0.01, CEACAM5 r=-0.51, p < 0.01). All three genes positively correlated with prospective exacerbations in both cohorts (IMSA: MUC1 r = 0.345, p = 0.01, MUC4 r = 0.216, p = 0.08, CEACAM5 r = 0.368, p < 0.01; SARP: MUC1 r = 0.22, p = 0.02, MUC4 r = 0.32, p < 0.01, CEACAM5 r = 0.38, p < 0.01). Conclusions The expression of MUC1, MUC4 and CEACAM5 increased with asthma severity in the airway epithelium and correlated with both prospective exacerbations and obstruction. As pathway analysis of genes in the significant latent factors were associated with airway keratinization aberrant expression of these mucins (with known signaling functions) may contribute to maladaptive repair and airway remodeling that drives obstruction over time, contributing to worse asthma outcomes. This abstract is funded by: NIH

Abstract Rationale The activity of fucosyltransferase 2 (FUT2) determines if mucin glycan structures in epithelial mucus include histo-blood group antigens (HBGAs). People with active FUT2 express HBGAs in epithelial mucus secretions and are terms “secretors”, while non-secretors lack HBGAs in their secretions because they have a FUT2 genotype that inactivates the glycosyl transferase. Prior research suggests that secretors who are blood type O (type O secretors) are susceptible to asthma exacerbations1 and that FUT2 knockout mice (functional non-secretors) are protected from mucus plugging in allergen challenge models2,3. We set out here to determine if secretor status influences mucus plug prevalence in asthma and to confirm if type O secretors are susceptible to asthma exacerbations. Methods We determined secretor status in asthma participants from the Severe Asthma Research Program-3 (SARP-3) cohort (N = 507) in two ways, a specific fucose lectin binding assay in sputum and FUT2 genotyping. Blood group type was determined using ABO genotyping. We analyzed mucus plug segment scores, asthma exacerbations rates and other clinical and biological features in patients stratified by secretor status and blood type (non-secretors, type O secretors, and non-type O secretors). Results Secretor status determined by lectin binding in sputum was strongly concordant with genotypic analysis. Within the SARP-3 cohort, 26.2% were non-secretors, 32.3% type were O secretors, and 41.4% were non-type O secretors. Mucus plug segment scores, annualized asthma exacerbation rates, and other measures of asthma severity were similar in non-secretors, type O secretors, and non-type O secretors (Table). Although type O secretors had increased values for fractional exhaled nitric oxide (FeNO) and higher expression of type 2 gene network genes in their sputum cells, measures of sputum eosinophil inflammation were not higher in this subgroup (Table). Conclusion Secretor status does not influence the prevalence of mucus plugging in asthma patients, and we did not confirm a prior report that type O secretors have an increased risk of asthma exacerbation. Although type O secretors have modestly increased FeNO levels and increased expression of type 2 immune genes in their sputum, it is not clear if this is a biologically important signal. 1. Innes et al. AJRCCM; 2011. 2. Saku et al. JACI; 2019. 3. Hara et al. AJRCMB; 2025 This abstract is funded by: The study was supported by the National Institutes of Health grants R01 HL080414 (JVF), P01 HL107202 (JVF), R01 HL164787 (JVF), U10 HL109172 (EI), U10 HL109152 (SEW), U10 HL109257 (MC), U10 HL109250 (SCE), U10 HL109146 (JVF), U10 HL109164 (ERB), U01 HL146002 (BDL), U10 HL109086 (DTM) and Sandler Asthma Basic Research Center at UCSF (JVF). The following companies provided financial support for study activities at the Coordinating and Clinical Centers beyond the third year of patient follow-up: AstraZeneca, Boehringer-Ingelheim, Genentech, GlaxoSmithKline, Sanofi–Genzyme Regeneron, and Teva. These companies had no role in study design or data analysis, and the only restriction on the funds was that they be used to support the SARP initiative.

Abstract Rationale We hypothesize that corticosteroid resistance causes uncontrolled inflammation and severe asthma. The genetic and molecular mechanisms underlying steroid responsiveness in asthma remain poorly understood (PMID28493293). This study aims to characterize transcriptomic profiles distinguishing steroid responders from steroid resistant asthma. Methods Longitudinal bulk RNA-seq of SARP3 sputum samples was analyzed before and after an “induced phenotype” with 40 mg triamcinolone acetonide (TCA) injection (PMID 27967215). Participants were classified as responders or non-responders based on whether their FEV₁ change after TCA exceeded the median. Paired differential gene expression analyses were performed separately for each group using limma and voom, with participant as a factor and adjustment for sputum cell count differentials. Z-scores were calculated to compare gene expression changes after TCA injection between responders and non-responders, and pathway enrichment was assessed using the fgsea package. Results Baseline demographics and clinical characteristics of 696 SARP3 asthma participants receiving TCA are shown in Table 1. The median [IQR] FEV1 change post-TCA was 1.81% [-2.16, 7.17]. Responders had higher baseline FEV1%, FEV1/FVC ratio, blood eosinophil counts, and sputum eosinophil percentages, but lower serum CRP levels. Steroid responsiveness was associated with asthma severity (Table 1). Among 154 participants with paired sputum RNA-seq data, 70 (45%) exhibited >1.81% improvement in FEV₁ and were classified as responders. Following TCA treatment, non-responders showed no significant changes in gene expression. In responders, 18 genes were upregulated and 203 downregulated. Downregulated genes were associated with Th2 immunity (IL13, IL1RL1, CCL17, SIGLEC8), IgE signaling (FCER1A, FCER2), epithelial barrier function and mucus production (MUC2, MUC7, ALOX15, TFF3), tissue remodeling and fibrosis (MMP10, TIMP3), ciliary function (DNAH5, CFAP43, FOXJ1), and airway hyperreactivity (HRH4, RAMP1). Key genes notably downregulated in responders compared to non-responders included IL13, CCL5, PTGDR2, FCER2, and CLEC10A. Pathway analysis revealed enhanced IL-10-mediated anti-inflammatory signaling, suppression of pro-inflammatory pathways (NF-κB, IL-1, Th1/Th2, asthma, arachidonic acid metabolism, chemokine, NOTCH4), and regulation of mitochondrial oxidative phosphorylation. Conclusions Steroid resistance impairs glucocorticoid-mediated suppression of pro-inflammatory pathways, including NF-κB, IL-1, and Th1/Th2 signaling. This persistent airway inflammation limits improvements in lung function and contributes to worse clinical outcomes, including increased airflow obstruction, and symptom burden. Glucocorticoid resistance in asthma may be driven by receptor dysfunction, airway inflammation, epigenetic changes, and environmental exposures resulting in persistent airway inflammation and remodeling. Elucidating the molecular mechanisms underlying steroid resistance is critical for developing personalized targeted therapies in asthma. This abstract is funded by: NIH-NHLBI - R01 HL161674 (PI: Joe Zein)

Abstract Rationale Asthma contributes substantially to healthcare burden and morbidity through frequent exacerbations. Emerging evidence suggests that genetic factors play a crucial role in modulating susceptibility to asthma exacerbations. To better understand the genetic architecture of exacerbations, we conducted a genome-wide association study (GWAS) in the Tapestry cohort. Methods The Tapestry Study, a large-scale, decentralized and clinical grade genomic sequencing study, conducted Exome+® sequencing at Helix, Inc. on 98,075 Mayo Clinic participants. After excluding patients with ≥10 pack-years of smoking and/or emphysema, we performed a GWAS of asthma exacerbations in 3,960 adults with asthma based on ICD codes. Cases (n = 1,059) were defined as individuals who experienced at least two exacerbations between 2020 and 2025; the remaining 2,901 individuals served as controls. Asthma exacerbations were defined by oral or systemic corticosteroid prescriptions with durations ranging from 3 days up to 28 days. Logistic regression models adjusted for age, sex, BMI, and the first six principal components of ancestry. Replication was performed in 1,273 asthma patients (439 African Americans and 834 non-Hispanic Whites) from the NHLBI-sponsored Severe Asthma Research Program (SARP 1-3), with adjustments for age, sex, BMI, and the first 10 principal components of ancestry. Results Based on a minor allele frequency (MAF) threshold of > 0.05, we analyzed 5,256,135 genome-wide variants. Genome-wide significant associations for asthma exacerbations (p < 5.0 × 10⁻8) included loci at a pseudogene in SMPD4P1 (rs680548, MAF = 0.39, OR = 1.37, p = 9.10 × 10⁻9). Additional variants showing suggestive associations included loci within ENDOD1 (rs638776, OR = 0.69, p = 1.20 × 10⁻6), PCSK2 (rs2206454, OR = 1.32, p = 3.53 × 10⁻6), RBFOX1 (rs17667084, OR = 0.60, p = 5.11 × 10⁻6), and CDC42EP3 (rs721660, OR = 1.29, p = 5.68 × 10⁻6). Subthreshold associations in Tapestry including loci at CDC42EP3 (rs4670213, OR = 1.27, p = 1.41x10-5, MAF = 0.36), and SDR39U1 (rs12587663,OR = 0.83, p = 5.86x10-4, MAF = 0.46) were replicated in the SARP longitudinal visit 5 with p-values of 8.523x10-3 (rs4670213, OR = 1.78), and 2.88x10-4 (rs12587663,OR=0.43), respectively. Conclusion Our GWAS for asthma exacerbations in the Tapestry cohort identified variant loci relevant to mitophagy mechanisms (CDC42EP3, PMID: 40783597), immune signaling and RNA splicing regulation (RBFOX1, PMID: 31301374), and neuromodulatory pathways (PCSK2, PMID: 32794589), all previously implicated in asthma pathophysiology. Collectively, these findings highlight potential novel genetic contributors to asthma exacerbations and provide a foundation for improving risk stratification and therapeutic targeting in asthma management. This abstract is funded by: This abstract is funded by: Mayo Clinic Funding: X01 from the NHLBI for TOPMed whole-genome sequencing and NIH grants R01 HL142992, HL69116, HL69167, HL69170, HL69174, U10 HL109164, U10 HL109257, U10 HL109146, U10 HL109172, U10 HL109250, U10 HL109250, U10 HL109250, U10 HL109168, U10 HL109152, U10 HL109086, U10 HL109046.

Importance Standard adjuvant therapy for human papillomavirus–associated oropharyngeal squamous cell carcinoma (HPV-OPSCC) is radiation therapy 60 Gy with or without cisplatin delivered in 30 fractions during 6 weeks. A phase 3 randomized clinical trial demonstrated decreased toxic effects and improved patient-reported outcomes with de-escalated adjuvant radiation therapy (DART) compared with standard therapy; however, outcomes for patients treated in the clinical practice setting following trial adoption remain unknown. Objective To compare characteristics and oncologic outcomes of patients treated with DART during clinical trials (on study) and in clinical practice settings (off study) and report progression-free survival (PFS) by risk category. Design, Setting, and Participants This retrospective cohort study included patients treated with DART in the MC1273 and MC1675 trials and in clinical practice after study completion at a multisite tertiary care center. Patients with surgically resectable HPV-OPSCC who underwent margin-negative resection between August 20, 2013, and March 21, 2023, and were treated with DART were included in the analysis. Those with prior head and neck cancer, pT0 or pT4 disease, unknown HPV status, metastatic disease at presentation, synchronous primary tumors, induction chemotherapy, or treatment at an outside institution were excluded. Data were analyzed from July 1, 2024, to July 18, 2025. Interventions DART consisting of 30 to 36 Gy in 1.5- to 1.8-Gy fractions twice daily with docetaxel 15 mg/m 2 on days 1 and 8. Main Outcomes and Measures Progression-free survival as measured via Kaplan-Meier analysis. Results A total of 282 patients were included in the analysis: 176 (62.4%) in the on-study group and 106 (37.6%) in the off-study group (252 [89.4%] male; mean [SD] age, 59.1 [9.3] years). Both groups were predominantly male (157 [89.2%] and 95 [89.6%], respectively) and consisted mostly of never smokers (118 [67.0%] and 62 [58.5%], respectively). Pathologic features were similar between groups except for nodal stage (pN1: 155 [88.1%] on study vs 102 [96.2%] off study; pN2: 21 [11.9%] on study vs 4 [3.8%] off study; P = .02). The median follow-up times were 5.2 years (95% CI, 5.2-5.8 years) in the on-study group and 2.2 years (95% CI, 1.9-2.4 years) in the off-study group. Two-year PFS was similar (93% [95% CI, 88%-97%] on study vs 93% [95% CI, 88%-99%] off study). For patients with pN1 and no extranodal extension (ENE), 2- and 5-year PFS were 97% (95% CI, 93%-100%) and 96% (95% CI, 92%-100%), respectively. Patients with pN1 and ENE had a 2- and 5-year PFS of 93% (95% CI, 89%-98%) and 87% (95% CI, 81%-94%), respectively. Conclusions and Relevance In this retrospective cohort study of patients receiving DART on and off study, oncologic outcomes were similar between the 2 groups. Fewer patients with pN2 received DART off study, given the interim results of MC1675. Patients with pN1 and no ENE treated with DART had excellent 2- and 5-year PFS, supporting DART as a compelling treatment option in well-selected patients. An additional study that is currently underway will evaluate biomarker risk-stratified treatment of patients with pN1 and ENE receiving DART.