B32-39 Disease Burden and Blood Eosinophils in Chinese Patients With Severe Eosinophilic Asthma: Baseline Analysis of a Phase IIIb Study of Step-down Maintenance Therapy (step)

Abstract Rationale Severe eosinophilic asthma (SEA) imposes heavy disease burden and benralizumab has shown efficacy in reducing background therapy while maintaining disease control in patients with SEA in global studies. STEP is the first study investigating the background therapy step-down in Chinese SEA patients treated with benralizumab. In this baseline analysis of STEP, we describe the disease burden and its association with the level of blood eosinophils (bEOS) upon study enrolment. Methods STEP (NCT06465485) is a single-arm, phase IIIb trial conducted across 76 Chinese sites. Eligible patients were 12-75 years old while fulfilling the following criteria: 1): bEOS ≥300 cells/μL, or bEOS between 150-300 cells/μL at enrolment and ≥300 cells/μL within one year before enrolment; 2): ≥1 exacerbation in the prior year; 3): on stable medium- or high-dose (MD/HD) inhaled corticosteroids-long-acting β2-agonist (ICS-LABA) for ≥2 month; MD patients could also receive leukotriene receptor antagonists (LTRA) or long-acting anti-muscarinic (LAMA). Results From February 28, 2024 to March 18, 2025, 489 patients were enrolled. Mean (SD) age was 48.2 (13.8) years; 204 (41.7%) patients were male; 30 (6.2%) were early-onset asthma (diagnosed before 18-years old) and 263 (54.2%) were late-onset asthma (diagnosed after 40-years old). Comorbidities included allergic rhinitis (254, 51.9%), nasal polyps (34, 7.0%) and atopic dermatitis (11, 2.2%). Among patients with available data, 56.2% (264/470) had Asthma Control Questionnaire (ACQ-5) score 1.5; 56.4% (276/489) had pre-bronchodilator (BD) forced expiratory volume in 1 second (FEV1)%pred 80%; 22.9% (112/489) had both ACQ-5 score 1.5 and pre-BD FEV1%pred 80%. Post-BD FEV1/forced vital capacity (FVC) 70% was observed in 46.2% (97/210) of patients. Overall, 77.5% (379/489) of patients had bEOS ≥300 cells/μL, including 69.3% (339/489) with co-elevation of fractional exhaled nitric oxide (FeNO) ≥20 ppb and 57.5% (281/489) with an additional co-elevation of Immunoglobin E (IgE) ≥60 IU/mL. When stratified by baseline bEOS level, patients with higher bEOS levels exhibited heavier disease burden (Table). Conclusions Although all patients experienced asthma exacerbations in the past one year, around 50% exhibited well-controlled symptoms at baseline based on an ACQ-5 score below 1.5. This suggested that relying solely on self-reported symptom control by ACQ-5 score may be inadequate for asthma assessment, potentially leading to under-treatment. Co-elevation of bEOS, FeNO and IgE were common. High bEOS level might be associated with heavy disease burden in these patients. This abstract is funded by: AstraZeneca China